Magnetic torque limiter

Abstract

Magnetic torque limiter This limiter is capable, in an engaged state, of transmitting, by magnetic coupling, the torque of a driving part to a driven part and, in a disengaged state, of allowing the rotational movement of the driving part without rotating the driven part. This limiter comprises: – a first ring (42) comprising a magnetic field source (52) capable of generating, on a first annular face of this first ring, an alternation of south poles and north poles, and – a second ring (44) comprising a second annular face (60) facing the first ring and a hoop (66) fixed, without any degree of freedom, on its second annular face (60), so as to be crossed by the magnetic field generated by the magnetic field source (52), this first hoop being made of an electrically conductive material. Fig. 3

Description

Title of the invention: Magnetic torque limiter

[0001] The invention relates to a magnetic torque limiter and to an electrical machine comprising this magnetic torque limiter.

[0002] Electrical machines comprising magnetic torque limiters are, for example, known from applications US4808869A and US3320448A. More specifically, applications US4808869A and US3320448A disclose motors in which the magnetic torque limiter is interposed between the rotor of the motor and the output shaft of the motor. Thus, during normal operation, the torque of the rotor is transmitted to the output shaft via the torque limiter. During normal operation, the rotor and the output shaft therefore rotate at the same speed. In the event of the output shaft being blocked in rotation, the limiter switches to a disengaged state where it allows the rotor to rotate while the output shaft is blocked. This makes it possible to avoid or limit damage caused by a sudden blocking of the rotation of the output shaft of the motor.For example, if the output shaft rotates a load through a set of gears, the presence of the torque limiter prevents damage to this set of gears by allowing the rotor to continue rotating under the effect of its inertia.

[0003] In the event of a shaft rotation lock, generally, the motor power supply is cut off to stop rotating the rotor. However, even when the motor power supply is cut off, due to the rotor's inertia, it takes some time for the rotor to come to a stop. For example, during this period of time when the rotor continues to rotate while the output shaft is locked, the limiter experiences alternating positive and negative detent torque caused by the fact that, as the rotor continues to rotate while the shaft is locked, south and north poles of the limiter alternately attract and repel each other. This causes undesirable phenomena such as vibrations that can accelerate wear of surrounding parts or create unwanted induced currents in the electronics.

[0004] The invention aims to remedy this drawback by proposing a magnetic torque limiter which makes it possible to limit such undesirable phenomena.

[0005] The invention therefore relates to a magnetic torque limiter intended to be placed between a driving part and a part driven in rotation around an axis of rotation, this magnetic torque limiter being capable of:

[0006] - in an engaged state, to transmit, only by magnetic coupling, the torque from the driving part to the driven part so that the driving and driven parts rotate at the same speed along the axis of rotation, and

[0007] - in response to the rotational blocking of the driven part, to automatically tilt tically in a disengaged state which allows the driving part to rotate without rotating the driven part,

[0008] this magnetic torque limiter comprising for this purpose a first and a second ring each mounted in rotation along the axis of rotation,

[0009] - the first ring comprising:

[0010] - a first annular face facing the second ring and whose axis of re volution is confused with the axis of rotation, and

[0011] - a first source of magnetic field capable of generating, on the first face annular, an alternation of south poles and north poles along a first circular trajectory centered on the axis of rotation, this first source of magnetic fields being fixed, without any degree of freedom, entirely behind the first annular face on the side opposite the second ring,

[0012] - the second ring comprising:

[0013] - a second annular face opposite the first annular face, this second annular face being turned towards the first ring and its axis of revolution being coincident with the axis of rotation, and

[0014] - elements capable of forming, on the second annular face, an alternation of poles south and north poles along a second circular path centered on the axis of rotation and located in the same plane as the first circular path, the number of south poles and north poles along the second path being identical to the number of south poles and north poles along the first path, these elements being fixed, without any degree of freedom, entirely behind the second annular face on the side opposite the first ring,

[0015] - an air gap located between the first and second annular faces, this air gap at allowing rotation of one of the rings while rotation of the other ring is blocked,

[0016] in which the second ring also comprises a first hoop fixed, without any degree of freedom, on the second annular face, so as to be crossed by the magnetic field generated by the first magnetic field source in the disengaged state, this first hoop being made of an electrically conductive material.

[0017] Embodiments of this limiter may include one or more of the following features:

[0018] 1)

[0019] - the elements capable of forming, on the second annular face, an alternation of poles south and north poles, comprises a second source of magnetic field capable of generating, on the second annular face, the alternation of south poles and north poles along the second circular path, and

[0020] - the first ring also has a second fixed fret, without any degree of freedom, on the first annular face, so as to be crossed by the magnetic field generated by the second magnetic field source in the disengaged state, this second hoop being made of an electrically conductive material.

[0021] 2) Each magnetic field source comprises at least one permanent magnet.

[0022] 3)

[0023] - the second ring surrounds the first ring, and

[0024] - the first and second annular faces are each cylindrical faces of which the direction curves are circles centered on the axis of rotation and whose generators are parallel to the axis of rotation.

[0025] 4) The first and second annular faces each extend in a radial plane respective perpendicular to the axis of rotation.

[0026] 5)

[0027] - the first ring comprises a first fixed magnetic crown, without any degree of freedom, on the side of the first magnetic field source opposite the first annular face and through which the field lines of the magnetic field generated by the first magnetic field source loop back, this first magnetic crown being centered on the axis of rotation, and

[0028] - the second ring comprises a second fixed magnetic crown, without any degree of freedom, on the side of the elements capable of forming on the second annular face an alternation of south poles and north poles, opposite the second annular face and through which the field lines of the magnetic field are looped back which form on the second annular face the alternation of south poles and north poles, this second magnetic crown being centered on the axis of rotation.

[0029] 6) The first source of magnetic field comprises permanent magnets arranged relative to each other to form a Halbach network which increases the magnetic field which passes through the first fret.

[0030] 7) The first fret is made of a non-magnetic material.

[0031] The invention also relates to an electrical machine comprising:

[0032] - a shaft mounted in rotation along an axis of rotation,

[0033] - a rotor mounted in rotation along the axis of rotation,

[0034] - a stator,

[0035] - a magnetic field source housed in one of the rotor and the stator for to transform electrical energy into a mechanical torque exerted on the shaft or to transform a mechanical torque exerted on the shaft into electrical energy,

[0036] - the above magnetic torque limiter housed between the rotor and the shaft, this limiter magnetic torque being suitable:

[0037] - in an engaged state, to transmit, only by magnetic coupling, the torque from one of the rotor and the shaft, to the other of the rotor and the shaft so that the rotor and the shaft rotate at the same speed along the axis of rotation, and

[0038] - in response to the rotational blocking of the shaft, to automatically switch into a disengaged state which allows the rotor to rotate without rotating the shaft,

[0039] this magnetic torque limiter comprising for this purpose a first and a second ring each mounted in rotation along the axis of rotation, one of this first and this second ring being fixed, without any degree of freedom, on the shaft, and the other of this first and this second ring being fixed, without any degree of freedom, to the rotor, the second ring being housed inside the rotor and surrounding the first ring,

[0040] - the first ring comprising:

[0041] - a first cylindrical face whose directrix curve is a circle centered on the axis of rotation and whose generator is parallel to the axis of rotation, and

[0042] - a first source of magnetic field capable of generating, on the first face cy lindric, an alternation of south poles and north poles along a first circular trajectory centered on the axis of rotation, this first source of magnetic fields being fixed, without any degree of freedom, entirely behind the first cylindrical face on the side opposite the second ring,

[0043] - the second ring comprising:

[0044] - a second cylindrical face whose directrix curve is a circle centered on the axis of rotation and whose generator is parallel to the axis of rotation, and

[0045] - elements capable of forming, on the second cylindrical face, an alternation of south poles and north poles along a second circular path centered on the axis of rotation and located in the same plane as the first circular path, the number of south poles and north poles along the second path being identical to the number of south poles and north poles along the first path, these elements being fixed, without any degree of freedom, entirely behind the second cylindrical face on the side opposite the first ring,

[0046] - an air gap located between the first and second cylindrical faces, this air gap at allowing rotation of one of the rings while rotation of the other ring is blocked.

[0047] Embodiments of this machine may include one or more of the following features:

[0048] 1) The second ring comprises a magnetic crown centered on the axis of rotation and through which loops back:

[0049] - the field lines of the magnetic field which form, on the second face cy lindric, the alternation of south poles and north poles, and

[0050] - the field lines of the magnetic field source housed in the rotor or the stator.

[0051] 2) The machine is a permanent magnet motor.

[0052] The invention will be better understood on reading the description which follows, given solely by way of non-limiting example and made with reference to the drawings in which:

[0053] - figures 1 and 2 are illustrations, in perspective, of the architecture of the same motor, equipped with a first embodiment of a magnetic torque limiter, from two different points of view,

[0054] - [Fig.3] is a partial view in vertical section of the torque limiter of the figures 1 and 2,

[0055] - [Fig.4] is a partial view in vertical section of a second mode of rea installation of a torque limiter for the motor of figures 1 and 2,

[0056] - [Fig.5] is an illustration, in longitudinal section, of a third mode of rea installation of a torque limiter, and

[0057] - [Fig.6] is a schematic illustration of an annular face of the limiter of couple of [Fig.5].

[0058] In this description, the terminology, conventions and definitions of the terms used in this text are introduced in a chapter I. Then, detailed examples of embodiments are described in a chapter II with reference to the figures. In a chapter III, variants of these embodiments are presented. Finally, the advantages of the different embodiments are specified in a chapter IV.

[0059] Chapter I: Definitions, terminologies and conventions:

[0060] In the figures, the same references are used to designate the same elements.

[0061] In the remainder of this description, the characteristics and functions well known to those skilled in the art are not described in detail.

[0062] The figures are oriented relative to an orthogonal XYZ coordinate system, where the X and Y directions are horizontal and the Z direction is vertical. Terms such as "above", "below", "top", "bottom", "upper", "lower" are defined relative to the Z direction.

[0063] The YZ plane is a vertical plane parallel to the Y and Z directions of the XYZ reference frame.

[0064] The symbol “*” denotes scalar multiplication.

[0065] The direction of magnetization of a permanent magnet corresponds to the direction of the magnetic moment of this permanent magnet. It is therefore a vector quantity.

[0066] An electrically conductive material is a material whose conductivity electrical, at 20°C, is greater than 106 S / m and, preferably, greater than 3*106 S / m or 4*106 S / m.

[0067] An electrically insulating material is a material whose electrical conductivity, at 20°C, is less than 10 10 S / m or 10 14 S / m.

[0068] A non-magnetic material is a material whose absolute value of magnetic susceptibility is less than 103 and, preferably, less than 10 4 or 105. Typically, the maximum relative magnetic permeability of a non-magnetic material is less than ten and often between 0.5 and 1.5.

[0069] A permanent magnet is a part made of a hard magnetic material.

[0070] A hard magnetic material is a magnetic material whose coercive field is greater than 25 kA / m or 50 kA / m.

[0071] A soft magnetic material is a magnetic material whose coercive field Hc is less than 1000 A / m. An element made of soft magnetic material becomes magnetized when placed in a magnetic field generated by a magnetic field source.

[0072] The expression “an element made of a material A” or the expression “an element of material A” means that material A represents 90% or 95% of the mass of this element.

[0073] The expression “a part A mounted in rotation along an axis B” means that the part A rotates on itself around the axis B and that this axis B passes through the part A.

[0074] The expression "a part A mounted to rotate around an axis B" means that the part A rotates around the axis B and that this axis B does not necessarily pass through the part A.

[0075] The expression “field lines” more precisely designates the magnetic flux iso-density lines.

[0076] Chapter II: Examples of embodiments

[0077] Figures 1 and 2 show a motor 2. In this example, the motor 2 is a brushless three-phase synchronous motor. The motor 2 comprises a stator 4, a rotor 6 and an output shaft 8. The rotor 6 and the shaft 8 are mounted to rotate about an axis 9 of rotation colinear with the direction X. The rotor 6 is shown in more detail in [Fig.3]

[0078] The stator 4 drives the rotor 6 in rotation when it is powered. For this purpose, the stator 4 comprises stator windings 10 connected, via three wire connections 12 to 14, to a three-phase power source not shown in the figures. To simplify Figures 1 and 2, the reference 10 points to only a portion of the stator windings shown in these figures.

[0079] The rotor 6 is mounted in rotation along the axis 9 by means of respective bearings, for example, as described in application US4808869A.

[0080] The rotor 6 comprises permanent magnets 20 which interact with the windings 10 to drive this rotor in rotation along the axis 9 when the windings 10 are powered. These magnets 20 are uniformly distributed along the outer periphery of the rotor 6 and face the windings 10. Here, the magnetization direction of the magnets 20 is radial, that is to say that the south and north poles of each magnet 20 are aligned, one behind the other, along an axis parallel to the YZ plane and which intersects the axis 9 of rotation. Along a circular path, centered on the axis 9 and belonging to the outer periphery of the rotor 6, the magnets 20 form a regular alternation of south and north poles. For this, the magnetization directions of the magnets 20 are directed towards the axis 9 and, alternately, towards the stator 4.

[0081] The magnets 20 are separated from the stator 4 by an air gap which extends mainly between two cylindrical faces. Hereinafter, a cylindrical face designates a face whose directrix curve is a circle centered on the axis 9 and whose generator is parallel to the direction X.

[0082] The magnets 20 are fixed, without any degree of freedom, on an outer face 24 of a magnetic armature 26. The armature 26 is essentially a cylinder whose directrix curve is centered on the axis 9 and whose generatrix is parallel to the direction X. For example, the armature 26 is made of soft magnetic material. In any vertical plane, parallel to the plane YZ, the armature 26 extends continuously all around the axis 9 and therefore forms a magnetic crown 27 ([Fig. 3]) centered on the axis 9 and through which the field lines of the magnets 20 loop back. In [Fig. 3] to highlight the inner and outer limits of this crown 27, these limits are shown in dotted lines.

[0083] The shaft 8 is mounted to rotate along the axis 9 by means of respective bearings, for example, as described in application US4808869A. The rotor 6 can therefore rotate along the axis 9 independently of the shaft 8.

[0084] The shaft 8 extends along the axis 9. One end of the shaft 8 is mechanically connected to a driven part 30, for example, via a set 32 of gears. The part 30 is the part that is driven in rotation when the motor 2 is powered. To simplify [Fig.l], the mechanical connection between the shaft 8, the part 30 and the set 32 of gears is not shown in [Fig.l].

[0085] The shaft 8 is driven in rotation along the axis 9 by the rotor 6. Thus, in this embodiment, the rotor 6 is the driving part since it is this rotor 6 which turns the shaft 8.

[0086] To avoid damaging the gear set 32 in the event of sudden blocking of the rotation of the part 30, the shaft 8 is coupled to the rotor 6 via a magnetic torque limiter 40. Such a limiter 40 is also known as a synchronous magnetic torque limiter. The limiter 40 is shown in more detail in [Fig.3].

[0087] The limiter 40 is capable of switching automatically, when the braking torque exerted on the shaft 8 exceeds a predetermined threshold Sb from an engaged state to a disengaged state. In the engaged state, shown in Figures 1 to 3, the limiter 40 transmits, only by magnetic coupling, the torque from the rotor 6 to the shaft 8. In the engaged state, the rotor 6 and the shaft 8 rotate at the same speed along the axis 9. In the disengaged state, the limiter 40 allows the rotor 6 to rotate without driving the shaft 8 in rotation. For example, the threshold S1 is equal to 3.5 Nm.

[0088] For this, the limiter 40 comprises a concentric inner ring 42 and an outer ring 44.

[0089] The ring 42 is fixed, without any degree of freedom, to the shaft 8. The ring 42 comprises an annular face 50, a magnetic field source and an armature 54. Here, the face 50 is a cylindrical face whose diameter of the directrix curve is greater than the diameter of the shaft 8.

[0090] In this embodiment, the magnetic field source of the ring 42 consists of N permanent magnets 52. The permanent magnets 52 form, on the face 50, a regular alternation of N south poles and N north poles along a circular trajectory centered on the axis 9. For this, the magnets 52 are all entirely housed behind the face 50, that is to say here between the axis 9 and the face 50 and, in this embodiment, between the shaft 8 and the face 50.

[0091] In this exemplary embodiment, the number N is equal to four. To form these south and north poles, the ring 42 therefore comprises eight permanent magnets 52. In addition, here, the magnetization direction of each magnet 52 is radial, that is to say it extends along an axis contained in a vertical plane parallel to the YZ plane and which intersects the axis 9. Under these conditions, to form the alternation of south and north poles along the circular trajectory, the magnetization directions of the magnets 52 are directed towards the axis 9 and, alternately, in the opposite direction, that is to say towards the ring 44. Thus, along the periphery of the face 50, each magnet 52, whose magnetization direction is directed towards the ring 44, is located between two consecutive magnets 52 each having a magnetization direction directed towards the axis 9.

[0092] The armature 54 comprises housings in which the magnets 52 are received. On the side of the magnets 52 opposite the face 50, the armature 54 extends continuously around the axis 9 and along the axis 9 and forms a magnetic ring 55 which guides the magnetic field lines of the magnets 52. In addition, in this embodiment, the armature 54 forms only a single block of material with the shaft 8 which makes it possible to fix the ring 42 without any degree of freedom on the shaft 8. For example, the armature 54 and the shaft 8 are made of martensitic steel. In this particular context, to make the ring 55 which guides the field lines of the magnets 52 visible, the limits The internal and external crown 55 are shown in dotted lines in [Fig.3].

[0093] Here, each magnet 52 is flush with the face 50. For example, in this embodiment, the cross-section of each magnet 52 has substantially the shape of a trapezium whose smallest base is turned towards the axis 9. Each magnet 52 extends, in the X direction, over the entire length of the limiter 40. These magnets 52 are uniformly distributed around the axis 9. The armature 54 is flush with the face 50 between the magnets 52. In this case, the face 50 is formed by the faces of the magnets 52 turned towards the ring 44 and by the face of the armature 54 which is flush between the magnets 52.

[0094] The ring 42 also comprises a hoop 56 fixed, without any degree of freedom, on the face 50 to brake the rotor 6 in the disengaged state of the limiter 40. The hoop 56 covers the entire face 50. The hoop 56 is made of a conductive material. Here, the hoop 56 is made of copper. The thickness of the hoop 56, in the radial direction, is preferably less than 10*ô or 5* ô or ô, where ô is the skin thickness calculated as a function of the maximum electrical frequency of the eddy currents likely to circulate in the hoop 56. In addition, the hoop 56 retains the magnets 52 in their respective housings.

[0095] The ring 44 is integral with the rotor 6. The ring 44 comprises an annular face 60, a magnetic field source and the armature 26. The annular face 60 is also a cylindrical face.

[0096] In this embodiment, the armature 26 is common to the rotor 6 and to the ring 44. In particular, the same ring 27 is used for looping the field lines of the magnets 20 and the field lines of the magnetic source of the ring 44.

[0097] Here, the magnetic source of the ring 44 consists of permanent magnets 62. The permanent magnets 62 form, on the face 60, a regular alternation of N south poles and N north poles along a circular trajectory centered on the axis 9. The north and south poles of the ring 44 are arranged so that, in the engaged state, each of these poles is opposite a pole of the ring 42 of opposite polarity. Thus, in the engaged state, the rings 42 and 44 are magnetically coupled to each other so that they rotate at the same speed.

[0098] The number of magnets 62 is equal to the number of magnets 52. The magnets 62 are all housed behind the face 60, that is to say here between the face 60 and the ring 27. In this embodiment, the magnetization direction of each magnet 62 is radial and the magnets 62 are arranged around the axis 9 in a similar manner to what has been described for the magnets 52. Thus, to form the alternation of south and north poles along the periphery of the face 60, the magnetization directions of the magnets 62 are directed towards the axis 9 and, alternately, in the opposite direction, that is to say towards the stator 4. Thus, along the periphery of the face 60, each magnet 62, whose magnetization direction is directed towards the stator 4, is located between two consecutive magnets each having a direction of magnetization directed towards axis 9.

[0099] The armature 26 comprises housings in which the magnets 62 are received. Here, each magnet 62 is flush with the face 60. For example, in this embodiment, each magnet 62 has substantially the shape of a tile which extends, in the direction X, over the entire length of the limiter 40. These magnets 62 are uniformly distributed around the axis 9. The armature 26 is flush with the face 60 between the magnets 62. In this case, the face 60 is formed by the faces of the magnets 62 facing the ring 42 and by the face of the armature 26 which is flush between the magnets 62.

[0100] The ring 44 also comprises a hoop 66 fixed, without any degree of freedom, on the face 60. The hoop 66 covers the entire face 60. The hoop 66 is made of a conductive material, for example, non-magnetic. For example, here, the hoop 66 is made of copper. The thickness of the hoop 66, in the radial direction, is, for example, identical to the thickness of the hoop 56. The hoop 66 retains the magnets 62 in their respective housings.

[0101] The hoop 66 is mechanically separated from the hoop 56 by a mechanical air gap 70. This air gap 70 allows the rotation of one of the rings 42, 44 relative to the other when the braking torque exerted on the shaft 8 exceeds the threshold Si. The thickness of the air gap 70 is typically greater than 0.1 mm.

[0102] During operation of the motor 2, the stator windings 10 are powered and generate a rotating magnetic field which, by magnetic coupling with the magnets 20, drives the rotor 6 in rotation. The rotation of the rotor 6 drives the rotation of the ring 44.

[0103] Initially, the limiter 40 is in its engaged state. In this state, the rotation of the ring 44 drives the ring 42 and therefore the shaft 8 into rotation. In the engaged state, the rings 42 and 44 rotate at the same speed so that the shaft 8 rotates at the same speed as the rotor 6. Since the rings 42 and 44 rotate at the same speed, the magnetic field passing through the hoops 56 and 66 is constant and does not vary over time. Under these conditions, no eddy current appears in either the hoop 56 or the hoop 66. Thus, in the engaged state, no energy is dissipated, by the Joule effect, by the hoops 56 and 66.

[0104] At a particular instant, the rotation of the part 30 is suddenly blocked. This causes the rotation of the shaft 8 and the ring 42 to be blocked. Even if the power supply to the motor 2 is immediately cut off in response to this blocking of the rotation of the part 30, the rotor 6 continues to rotate, by inertia, around the axis 9 while the shaft 8 is blocked. The limiter 40 is therefore in its disengaged state. In this disengaged state, the magnetic field which passes through the hoops 56 and 66 varies over time because of the relative displacement of the magnets 52 with respect to the magnets 62. Eddy currents therefore appear in the hoops 56 and 66. These eddy currents in cause the appearance of Laplace forces which oppose the rotation of the ring 44 and the rotor 6. In other words, these Laplace forces slow down the rotation of the ring 44 and the rotor 6. Thus, thanks to the frets 56 and 66, the rotation of the ring 44 stops more quickly than in a configuration without such frets such as that described in application US4808869A. The period of time during which undesirable phenomena appear in the limiter 40 is therefore reduced, which has the consequence of reducing its wear.

[0105] [Fig. 4] shows a limiter 80 identical to the limiter 40 except that the magnets 52 are replaced by magnets 82 and the magnets 62 are replaced by magnets 84. The magnets 82 are arranged relative to each other to form a Halbach array that maximizes the magnetic field generated on the side of the air gap 70 and minimizes the magnetic field generated on the side opposite the air gap 70. Similarly, the magnets 84 are arranged relative to each other to form a Halbach array that maximizes the magnetic field generated on the side of the air gap 70 and minimizes the magnetic field generated on the side opposite the air gap 70. The magnetization directions of the magnets 82 and 84 that allow a Halbach array to be formed are represented by arrows inside each of the magnets 82 and 84 on the [Fig.4]. In [Fig.4], the limiter 80 is shown in the engaged state.In this embodiment, the field lines of the magnetic field generated by the magnets 82 and 84 do not loop back through the rings 27 and 55 of the armatures 26 and 54. Thus, in this embodiment, the thickness of the rings 27 and 55 is reduced or these rings are eliminated.

[0106] The operation of the limiter 80 is identical to that of the limiter 40 except that the field lines of the magnets 82 and 84 do not loop back via magnetic rings such as rings 27 and 55.

[0107] Figures 5 and 6 show a magnetic torque limiter 100 which is mechanically connected between the facing ends of two shafts 102 and 104. The limiter 100 is not integrated inside a motor. The shafts 102 and 104 are mounted to rotate about an axis 106 parallel to the direction X. The shaft 102 drives the shaft 104 in rotation. Thus, in this embodiment, the shaft 102 corresponds to the driving part and the shaft 104 corresponds to the driven part.

[0108] The limiter 100 is designed to operate like the limiter 40 but in the case where it is used to couple the ends of the shafts 102 and 104. For this purpose, it comprises two rings 112 and 114 fixed, without any degree of freedom, to the ends of the shafts, respectively, 102 and 104.

[0109] The ring 112 comprises an annular face 120, a magnetic field source and an armature 124. In this embodiment, the annular face 120 is a disc centered on the axis 106 and which extends in a plane perpendicular to the axis 106. Ty stinging, the outside diameter of the face 120 is greater than the diameter of the shaft 102.

[0110] The magnetic field source of the ring 112 consists of N permanent magnets 122. The permanent magnets 122 form, in the face 120, a regular alternation of N south poles and N north poles along a circular trajectory centered on the axis 106. The magnets 122 are all housed behind the face 120, that is to say here on the side of the face 120 which comprises the shaft 102.

[0111] In this embodiment, the number N is equal to four. To form these south and north poles, the ring 112 comprises eight permanent magnets 122. The magnetization direction of each magnet 122 is axial, that is to say it is parallel to the axis 106. Under these conditions, to form the alternation of south and north poles in the face 120, the magnetization directions of the magnets 122 are directed towards the shaft 102 and, alternately, in the opposite direction, that is to say towards the ring 114. In Figures 5 and 6 the magnetization directions of the magnets 122 are represented by arrows. More precisely, in [Fig.6], a point surrounded by a circle indicates that the magnetization direction is perpendicular to the plane of the sheet and exits towards the front of the sheet. Conversely, a cross surrounded by a circle indicates that the direction of magnetization is perpendicular to the plane of the sheet and exits towards the back of the sheet.

[0112] The armature 124 comprises housings in which the magnets 122 are received. On the side of the magnets 122 opposite the face 120, the armature 124 extends continuously around the axis 106 and forms a magnetic crown 125 which guides the field lines of the magnets 122. In this exemplary embodiment, the armature 124 is fixed, without any degree of freedom, on the end of the shaft 102. The armature 124 is made of ferromagnetic material.

[0113] Here, each magnet 122 is flush with the face 120. For example, in this embodiment, each magnet 122 has substantially the shape of a wedge whose narrowest end is directed towards the axis 106. These magnets 122 are uniformly distributed around the axis 106. The armature 124 is flush with the face 120 between the magnets 122. In this case, the face 120 is formed by the faces of the magnets 122 facing the ring 114 and by the face of the armature 124 which is flush between the magnets 122.

[0114] The ring 112 also comprises a hoop 126 fixed, without any degree of freedom, on the face 120 to brake the shaft 102 in the disengaged state of the limiter 100. The hoop 126 covers the entire face 120. The hoop 126 is made of a conductive material. For example, the hoop 126 is made of copper. The thickness of the hoop 126, in the X direction, is preferably less than 10*ô or 5* ô or ô, where ô is the skin thickness calculated as a function of the maximum electrical frequency of the eddy currents likely to circulate in the hoop 126. In addition, the hoop 126 retains the magnets 122 in their respective housings.

[0115] The ring 114 is fixed, without any degree of freedom, on the end of the shaft 104 opposite the ring 112. The ring 112 and the ring 114 are separated from each other by an air gap 130 which allows the ring 112 to continue to rotate while the ring 114 is blocked in rotation.

[0116] Here, the ring 114 is symmetrical to the ring 112 with respect to a median plane of the air gap 130. In [Fig. 5] the reference numerals 140, 142, 144, 145 and 146 designate the following elements of the ring 114: the annular face, the permanent magnets, the armature, the magnetic crown and the hoop. In the engaged state shown in [Fig. 5], the magnetization directions of the magnets 142 are parallel and in the same direction as the magnetization directions of the magnets 122 opposite each other. Thus, each south pole of the face 120 is opposite a north pole of the face 140 and each north pole of the face 120 is opposite a south pole of the face 140.

[0117] In the disengaged state, the ring 112 moves in rotation relative to the ring 114 which generates eddy currents in the hoops 126 and 146 which slow the rotation of the ring 112.

[0118] Chapter III: Variants:

[0119] Variants of the magnetic field source:

[0120] Within the framework of this section, the variants are described in the particular case of the magnetic field source of the ring 42. However, all these variants are transposable to the magnetic field source of the other ring of the torque limiter and to the embodiment of figures 5 and 6.

[0121] The number N of south poles is at least one and can be two, three or more than four. The number of north poles is always identical to the number of south poles.

[0122] Other arrangements of the permanent magnets to form the alternation of south and north poles on the cylindrical face 50 are possible. An example of another possible arrangement of these magnets is for example described in application FR2766028A1. The permanent magnets can also be arranged so as to have a so-called “multipolar” or PMIM (“Permanent Magnet Induction Machine”) magnetization.

[0123] In another variant, only the permanent magnets of the ring 42 are arranged relative to each other to form a Halbach network.

[0124] Each permanent magnet 52 may be replaced by a coil that generates a magnetic moment in the same direction as the magnetization direction of the permanent magnet 52 that it replaces. In this case, the magnetic field source also includes an electrical connection that allows it to be electrically connected to an external power source. This external power source is mechanically located outside the ring 42. If the power source is a battery, this power source may also be housed inside the ring 42. inside the ring 42.

[0125] In a simplified variant, one of the rings is devoid of a magnetic field source. In this case, instead of a magnetic field source, the ring 42 has magnetic teeth to create a magnetic coupling between the rings 42 and 44 which functions like that of variable reluctance machines. For this, for example, each magnet 52 is replaced by a magnetic tooth of identical or similar shape. These teeth are not permanently magnetized. For this purpose, the teeth are made of a soft magnetic material. Between each tooth, the armature 54 is shaped to have a higher reluctance. For example, between each tooth, the armature has a hollow. The teeth are made, for example, of ferromagnetic material. The teeth and the armature 54 may form a single block of material.The magnetic teeth guide the field lines of the magnets 62 and form on the cylindrical face 50, in the presence of the magnets 62 and in the engaged state, an alternation of south and north poles similar to that formed by the magnets 52. In the engaged state, each tooth faces a respective magnet 62 so that the inner and outer rings rotate at the same speed. In the case where only one of the rings has a magnetic field source, the field lines which pass through the hoop fixed on the face of the ring equipped with the magnetic field source are then constant in the engaged state and in the disengaged state. Thus, this hoop does not contribute to braking in the disengaged state. Only the hoop fixed on the ring without a magnetic field source contributes to braking.

[0126] In another particular variant, only the magnets 52 whose magnetization directions point towards the axis 9 are replaced by magnetic teeth.

[0127] Torque limiter variants:

[0128] In a simplified embodiment, the armature 54 does not extend continuously around the axis 9 and therefore does not form the magnetic ring 27. In the absence of a magnetic ring and a particular configuration of the permanent magnets such as those shown in [Fig. 4], the field lines of the magnets 52 then loop back in the air instead of looping back via the ring 27. This variant also applies to the rings 44, 112 and 114.

[0129] The frets can be made of other conductive material such as silver, aluminum, gold and also zinc, iron and lead. In particular, as a variant the fret is made of a conductive material which is not non-magnetic.

[0130] Alternatively, one of the two frets 56 and 66 or one of the two frets 126 and 146 is omitted.

[0131] The limiter 40 is not necessarily implemented within the rotor of an electrical machine. For example, alternatively, the limiter 40 is used to couple the ends of a first and a second shaft together. For example, the first shaft is the output shaft of a motor that is devoid of a magnetic torque limiter. The second shaft is mechanically connected to the driven part. In this case, for example, the inner and outer rings are mechanically attached, without any degree of freedom, to the first and second shafts respectively.

[0132] Other variants:

[0133] Other embodiments of the motor 2 are possible. For example, as a variant, one magnet 20 out of two is replaced by a tooth made of ferromagnetic material. In the latter case, each of these teeth is located between two respective magnets 20. The magnetization of each magnet 20 can also be diametrical, that is to say contained in the YZ plane and perpendicular to the radius which passes through this magnet 20.

[0134] What has been described in the particular case of a permanent magnet synchronous motor also applies to other motor technologies such as direct current motors or alternating current motors such as universal, synchronous or asynchronous motors or even variable reluctance motors.

[0135] The teaching given here does not only apply to motors but, more generally, to any transmission of a mechanical torque from a rotating part to another rotating part. In particular, the teaching given here applies to any machine, whether electrical or not, and in particular to alternators which produce electrical energy from the rotation of their shaft. In this case, the driven part is the rotor of this alternator and the driving part is a part mechanically connected to the shaft of this alternator to drive it in rotation.

[0136] As a variant, the armature of the rotor 6 is distinct from the armature of the external ring 44. In the latter case, the armature of the ring 44 is fixed, without any degree of freedom, on the armature of the rotor 6 by fixing means such as screws.

[0137] The shaft 8 may be made of other materials and, in particular, of a non-magnetic material such as plastic. In this case, the shaft 8 and the magnetic crown of the ring 42, 112 or 114 are two separate elements mechanically connected to each other without any degree of freedom.

[0138] Several of the variants described above can be combined in the same embodiment.

[0139] Chapter IV: Advantages of the described embodiments:

[0140] When the limiter is in its disengaged state, the ring 44 can continue to rotate while the ring 42 is locked in rotation. This prevents damage to the driving and driven parts. In addition, in the disengaged state, when the ring 44 continues to rotate while the ring 42 is locked, the magnetic field passing through each hoop 56, 66 varies over time. Since each hoop is made of conductive material, this causes the appearance of eddy currents which, in turn, cause the appearance of Laplace forces which oppose the rotation of the ring 44. Thus, the presence of a conductive hoop makes it possible, in the disengaged state, to slow the rotation of the driving part and to dissipate energy by Joule effect in the conductive hoop. On the other hand, in the engaged state, the rings 42 and 44 rotate at the same speed. Thus, in the engaged state, the magnetic field which passes through each hoop 56, 66 is constant. Therefore, no eddy current appears and energy is not dissipated by Joule effect in the conductive hoops. Thus, when the conductive hoop is fixed on the cylindrical face of one of the rings, it makes it possible to dissipate energy to brake the driving part only when necessary, that is to say in the disengaged state. Since in the disengaged state, the rotation of the driving part is slowed, it stops rotating more quickly than in the absence of a conductive hoop.This shortens the time during which undesirable phenomena can occur, which limits wear on the torque limiter.

[0141] In addition, the conductive band reinforces the retention, inside the ring, of the elements capable of forming, on the annular face, an alternation of south poles and north poles. Thus, the limiter is more robust.

[0142] Using magnetic field sources in both rings increases the magnetic coupling between these two rings. In addition, in this case, fixing a conductive band on each of the annular faces strengthens the fixing of the magnetic sources of the two rings of the limiter. This therefore reinforces the strength of the magnetic torque limiter. This also makes it possible to obtain even more effective braking.

[0143] Using permanent magnets to form the magnetic field sources helps to limit the energy consumption of the torque limiter. In addition, it simplifies its design.

[0144] The fact that the annular faces are cylindrical faces whose generators are parallel to the axis of rotation makes it possible to simply house such a limiter inside the rotor of an electrical machine.

[0145] The fact that the annular faces each extend in a respective radial plane makes it easier to insert the limiter between the ends of two facing shafts.

[0146] Using a magnetic ring located on the side of the magnetic field source opposite the annular face facilitates the looping of the field lines and therefore improves the magnetic coupling between the two rings. In addition, when the torque limiter is implemented inside the rotor of a motor, this makes it possible to limit magnetic interference between the magnetic source of the torque limiter and the magnetic parts of the rotor which cooperate with the magnetic field generated by the stator to drive this rotor in rotation. In some cases, limiting or eliminating this magnetic interference is important to ensure optimal operation of the engine.

[0147] Arranging the magnets of one of the rings to form a Halbach array makes it unnecessary to use a magnetic ring to guide the looping of the field lines. This therefore simplifies the design of the torque limiter.

[0148] The fact that the same magnetic crown is used both for looping back the field lines of the magnetic field which forms the alternation of south and north poles on the cylindrical face 60 of the ring 44 and for looping back the field lines of the magnets 20 and windings 10, makes it possible to simplify the design of an electrical machine comprising a magnetic torque limiter.

Claims

Claims

1. Magnetic torque limiter intended to be placed between a driving part and a part driven in rotation around an axis of rotation, this magnetic torque limiter being capable: - in an engaged state, to transmit, only by magnetic coupling, the torque from the driving part to the driven part so that the driving and driven parts rotate at the same speed along the axis of rotation, and - in response to the rotational blocking of the driven part, to automatically switch into a disengaged state which allows the rotational movement of the driving part without rotating the driven part, this magnetic torque limiter comprising for this purpose a first and a second ring (42, 44; 112, 114) each mounted in rotation along the axis of rotation, - the first ring (42; 112) comprising: - a first annular face (50; 120) facing the second ring and whose axis of revolution coincides with the axis of rotation, and - a first source (52; 122) of magnetic field capable of generating, on the first annular face, an alternation of south poles and north poles along a first circular trajectory centered on the axis of rotation, this first source of magnetic fields being fixed, without any degree of freedom, entirely behind the first annular face on the side opposite the second ring, - the second ring (44; 114) comprising: - a second annular face (60; 140) facing the first annular face, this second annular face being turned towards the first ring and its axis of revolution being coincident with the axis of rotation, and - elements (62; 142) capable of forming, on the second annular face, an alternation of south poles and north poles along a second circular trajectory centered on the axis of rotation and located in the same plane as the first circular trajectory, the number of south poles and north poles along the second trajectory being identical to the number of south poles and north poles along the first trajectory, these elements being fixed, without any degree of freedom, entirely behind the second annular face on the side opposite the first ring, - an air gap (70; 130) located between the first and second faces an- annular, this air gap allowing the rotation of one of the rings while the rotation of the other ring is blocked, characterized in that the second ring (44; 114) also comprises a first hoop (66; 146) fixed, without any degree of freedom, on the second annular face (60; 140), so as to be crossed by the magnetic field generated by the first source (52; 122) of magnetic field in the disengaged state, this first hoop being made of an electrically conductive material.

2. Limiter according to claim 1, in which: - the elements capable of forming, on the second annular face, an alternation of south poles and north poles, comprise a second source (62; 142) of magnetic field capable of generating, on the second annular face (60; 140), the alternation of south poles and north poles along the second circular trajectory, and - the first ring also comprises a second hoop (56; 126) fixed, without any degree of freedom, on the first annular face (50; 120), so as to be crossed by the magnetic field generated by the second source of magnetic field in the disengaged state, this second hoop being made of an electrically conductive material.

3. A limiter according to any preceding claim, wherein each magnetic field source comprises at least one permanent magnet (52, 62; 82, 84; 122, 142).

4. Limiter according to any one of the preceding claims, in which: - the second ring (44) surrounds the first ring (42), and - the first and second annular faces (50, 60) are each cylindrical faces whose directrix curves are circles centered on the axis of rotation and whose generatrices are parallel to the axis of rotation.

5. A limiter according to any one of claims 1 to 3, wherein the first and second annular faces (120, 140) each extend in a respective radial plane perpendicular to the axis of rotation.

6. Limiter according to any one of the preceding claims, in which: - the first ring (42; 112) comprises a first magnetic crown (55; 125) fixed, without any degree of freedom, on the side of the first magnetic field source opposite the first annular face (50; 120) and by means of which the field lines of the magnetic field generated by the first magnetic field source, this first magnetic crown being centered on the axis of rotation, and - the second ring (44; 114) comprises a second magnetic crown (27; 145) fixed, without any degree of freedom, on the side of the elements capable of forming on the second annular face an alternation of south poles and north poles, opposite the second annular face (60; 140) and by means of which the field lines of the magnetic field are looped back which form on the second annular face the alternation of south poles and north poles, this second magnetic crown being centered on the axis of rotation.

7. A limiter according to any one of claims 1 to 5, wherein the first magnetic field source comprises permanent magnets (82) arranged relative to each other to form a Halbach array which increases the magnetic field passing through the first hoop (66).

8. Limiter according to any one of the preceding claims, in which the first hoop (66; 146) is made of a non-magnetic material.

9. Electrical machine comprising: - a shaft (8) mounted for rotation about an axis (9) of rotation, - a rotor (6) mounted for rotation about the axis (9) of rotation, - a stator (4), - a magnetic field source (10, 20) housed in one of the rotor and the stator to transform electrical energy into a mechanical torque exerted on the shaft or to transform a mechanical torque exerted on the shaft into electrical energy, - a magnetic torque limiter (40) housed between the rotor and the shaft, this magnetic torque limiter being capable: - in an engaged state, of transmitting, only by magnetic coupling, the torque of one of the rotor and the shaft, to the other of the rotor and the shaft so that the rotor and the shaft rotate at the same speed about the axis of rotation, and - in response to the rotational blocking of the shaft, of automatically switching into a disengaged state which allows the rotational movement of the rotor without driving the shaft into rotation,this magnetic torque limiter comprising for this purpose a first and a second ring (42, 44) each mounted in rotation along the axis of, rotation, one (42) of this first and this second ring being fixed, without any degree of freedom, on the shaft, and the other (44) of this first and this second ring being fixed, without any degree of freedom, to the rotor, the second ring being housed inside the rotor and surrounding the first ring, - the first ring (42) comprising: - a first cylindrical face (50) whose directrix curve is a circle centered on the axis of rotation and whose generator is parallel to the axis of rotation, and - a first source (52) of magnetic field capable of generating, on the first cylindrical face, an alternation of south poles and north poles along a first circular trajectory centered on the axis of rotation, this first source of magnetic fields being fixed, without any degree of freedom, entirely behind the first cylindrical face on the side opposite the second ring, - the second ring (44) comprising: - a second cylindrical face (60) whose directrix curve is a circle centered on the axis of rotation and whose generator is parallel to the axis of rotation, and - elements (62) capable of forming, on the second cylindrical face, an alternation of south poles and north poles along a second circular trajectory centered on the axis of rotation and located in the same plane as the first circular trajectory, the number of south poles and north poles along the second trajectory being identical to the number of south poles and north poles along the first trajectory, these elements being fixed, without any degree of freedom, entirely behind the second cylindrical face on the side opposite the first ring, - an air gap (70) located between the first and second cylindrical faces (50, 60), this air gap allowing the rotation of one of the rings while the rotation of the other ring is blocked, characterized in that the magnetic torque limiter (40) conforms to any one of the preceding claims.

10. Machine according to claim 9, in which the second ring (44) comprises a magnetic crown (27) centered on the axis of rotation and by means of which loops back: - the field lines of the magnetic field which form, on the second cylindrical face (60), the alternation of south poles and north poles, and - the field lines of the magnetic field source (10, 20) housed in the rotor or stator.

11. A machine according to claim 10, wherein the machine is a permanent magnet motor.

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