ROTATING ELECTRIC MACHINE

Description

[0001] The present invention relates to the field of rotating electrical machines, and more particularly but not exclusively those used for the motorization of robots.

[0002] Application EP 1 793 482 relates to a rotating electrical machine with reduced torque ripple under load, which is intended for driving elevator cabins, and comprises an outer rotor having substantially flat faces directed towards the stator.

[0003] US 2008 / 157619 relates to an external rotor machine, in which the rotor comprises permanent magnets of generally cylindrical shape, the surface of which facing the internal stator is of concave shape.

[0004] In US 6,727,630, the rotor is external and an attempt is made to provide a variable spacing with the surface of the internal stator.

[0005] US application 2012 / 126654 relates to a motor having a permanent magnet rotor which includes notches to reduce magnetic cogging.

[0006] WO 2015 / 068749 relates to a rotor whose permanent magnets are flat or convex towards the stator.

[0007] DE 10 2014 222064 relates to a rotor whose permanent magnets are convex towards the stator.

[0008] Rotating electrical machines with an external rotor are also known, in which the permanent magnets of the external rotor have a main face directed towards the stator, of cylindrical shape of revolution.

[0009] In the case of an inner rotor, the main face of a magnet facing the stator is generally convex in shape.

[0010] However, particularly in the field of robot motorization, it may be necessary to reduce the magnetic cogging of a rotating electrical machine, particularly for example for a permanent magnet motor driven by a frequency converter. Magnetic cogging is also called detent torque (" cogging » in English), and corresponds to a torque ripple at no load or very low load.

[0011] There is therefore a need, particularly in the field of robot motorization, to have rotating electrical machines with low torque ripple under no-load or very low load.

[0012] The invention aims to meet all or part of this need and has as its subject, according to one of its aspects, a rotating electrical machine as defined in claim 1.

[0013] The presence of a generally concave face directed towards the stator for the rotor's permanent magnets makes it possible to optimize torque ripples at no-load or very low load.

[0014] We can thus seek to minimize torque ripples while obtaining a minimum peak torque to be achieved, for a pre-fixed mechanical air gap.

[0015] In addition, the rotor has a better ability to resist demagnetization. Rotor

[0016] By "generally concave face" is meant that the face of the permanent magnets of the rotor facing the stator has a curvature giving it a hollow surface. The face has one or more concave portions and one or more flat portions.

[0017] The presence of flat portions can help to better avoid interference between the rotor and the stator.

[0018] In one embodiment, the rotor may be internal. In this case, the face of the magnets facing the stator corresponds to the face of the magnets opposite an axis of rotation X of the machine.

[0019] Alternatively, the rotor can be external, which can allow it to rotate at a relatively high speed while limiting the risk of the magnets becoming detached. In this case, the face of the magnets facing the stator corresponds to the face of the magnets facing the X axis of rotation of the machine.

[0020] In the case of an external rotor, the concavity of the stator-facing face of the rotor's permanent magnets is greater than a concavity imparted solely by a cylindrical shape of the face, which would be due to the external arrangement of the rotor to allow the stator to be placed inside it and to provide a sufficient air gap between the rotor and the stator. In other words, the concavity of the stator-facing faces of the rotor's permanent magnets is deeper than a cylindrical surface of revolution.

[0021] The rotor shaft can be solid, for example hollow or solid.

[0022] Alternatively, it could be made of a non-solid material, for example a stack of laminated sheets. The sheets can each be coated with an insulating varnish to limit losses due to induced current.

[0023] A concave face of a rotor permanent magnet may have a concave portion. The widthl of the concave portion, measured perpendicular to a radius of the rotor, is between 0.1π(DS -2 d ) / P and 2π(DS -2 d ) / P mm (millimeters),

[0024] Where DS is the stator bore diameter, P the number of rotor poles, and d the simple air gap, that is to say the smallest width of the air gap.

[0025] The width l of the concave portion, measured perpendicular to a radius of the rotor, can be between 2 and 56 mm, better between 4 and 40 mm, or even between 8 and 20 mm, even better between 8 and 12 mm.

[0026] A width of a permanent magnet of the rotor measured perpendicular to the axis of rotation is for example between 0.1π(DS -2 d ) / P and 2 π (DS -2 d ) / P mm (millimeters).

[0027] The width of a permanent magnet of the rotor measured perpendicular to the axis of rotation is for example between 4 and 56 mm, better between 6 and 50 mm, or even between 8 and 40 mm, even better between 10 and 20 mm, being for example of the order of 13 mm.

[0028] The greatest depth p the concavity of the concave portion, measured along a radius of the rotor, may be between 0.01 mm and the thickness h of the corresponding magnet, in particular between 0.05 and 3 mm, or even between 0.1 and 1.5 mm.

[0029] The greatest depth of the concavity of the concave portion, measured along a radius of the rotor, may be located at the midpoint of the concave face of the corresponding permanent magnet. A permanent magnet is preferably symmetrical about a plane intersecting it in its middle, this plane passing through the axis of rotation of the machine and a radius of the rotor. Alternatively, the greatest depth of the concavity of the concave portion, measured along a radius of the rotor, is located elsewhere than at the midpoint of the concave face of the corresponding permanent magnet. A permanent magnet may not be symmetrical about a plane intersecting it in its middle.

[0030] The concave portion can be in section a portion of a circle or ellipse. The radius of the circle or the major axis of the ellipse can be included for example between 0.1 h *, Or h is the thickness of the magnet, and 100 hmm, in particular between 4 and 56 mm, better between 6 and 40 mm, being for example of the order of 13 mm.

[0031] The concave portion of a concave face is arranged between two flat lateral portions. The presence of flat lateral portions on the generally concave face makes it possible to benefit from the advantage of the concavity for the face of the magnets facing the stator, while having a sufficient air gap between the rotor and the stator.

[0032] The width of a flat lateral portion measured perpendicular to a radius of the rotor is for example between 0 and the width L of the magnet, better between 0.75 and 7 mm, being for example of the order of 2 mm.

[0033] The concave portion may constitute from 20 to 100% of the total width of the corresponding magnet, better between 25 and 90%, or even between 40 and 80%. In one embodiment, the concave portion constitutes 75% of the total width of the corresponding magnet. In another embodiment, in the absence of a planar lateral portion, the concave portion constitutes 100% of the total width of the corresponding magnet.

[0034] The permanent magnets of the rotor have, when the machine is observed along the axis of rotation, an elongated cross-section. In particular, the permanent magnets of the rotor may have, when the machine is observed along the axis of rotation of the rotor, a generally rectangular cross-section with the long side oriented perpendicular to a radius of the machine.

[0035] The rotor's permanent magnets can have a thickness h, measured according to a rotor radius, between 0.5 and 32d, Or d is the smallest width of the air gap, in particular between 1 and 20 mm, better between 2 and 10 mm, or even between 3 and 5 mm.

[0036] A ratio p / h between the greatest depth of the concavity of the concave portion, measured along a radius of the rotor, and the thickness of a permanent magnet is for example between 0.01 and 0.9, better between 0.1 and 0.4.

[0037] The rotor and the stator provide an air gap between them. The air gap may have a width, measured along a radius of the machine, of between 0.5 and 3 mm, better between 0.6 and 1.4 mm, for example being of the order of 0.9 mm. The air gap is preferably greater than 5 / 10 mm, better greater than 7 / 10 mm, in order to allow rotation of the rotor in or around the stator.

[0038] The width d 0 of the air gap, measured along a radius passing through the middle of a magnet, can be between 0.5 and 5 mm, better between 0.75 and 3 mm, being for example of the order of 1.6 mm. The air gap can be at its widest in the middle of a magnet, for the machine according to the invention, insofar as the concavity of the concave face of the magnet is deepest there.

[0039] The rotor bore DR, which corresponds to the outer diameter of the rotor in the case of an internal rotor, is for example between 15 and 100 mm, better between 20 and 70 mm, being for example of the order of 65 mm.

[0040] The magnets may or may not be monolithic. In one embodiment, a rotor pole is formed from a single permanent magnet. Alternatively, a rotor pole is formed from multiple magnets that may be arranged one after the other as one moves along the rotor's axis of rotation.

[0041] Permanent magnets can be made of ferrites, plastoferrites, rare earths or plasto-rare earths, or AlNiCo.

[0042] Permanent magnets can be formed from powder and then machined.

[0043] The remanent induction in the permanent magnets of a rotor pole can be between 0.2 Tesla and 1.5 Tesla, better between 0.3 Tesla and 1.3 Tesla, being for example of the order of 1.2 Tesla.

[0044] The permanent magnets of the rotor have a mounting face opposite the concave face facing the stator. The mounting face may be flat. A flat face may facilitate the installation of the magnets on the shaft. Alternatively, the mounting face could be convex, which may improve the electromagnetic performance of the machine. The convexity of the mounting face may be directed toward the axis of rotation in the case of an inner rotor, or outward in the case of an outer rotor, which may improve the electromagnetic performance of the machine.

[0045] In the case of a flat face, the flat face is oriented perpendicular to the ray passing through the axis of rotation and intersecting the corresponding magnet at mid-length.

[0046] The permanent magnets can be attached to the rotor shaft by gluing, for example to a cylindrical surface of the shaft or in a recess provided for this purpose on the surface of the shaft. Alternatively, they can be crimped into a corresponding recess in the shaft. The recess can have a flat or concave surface, depending on the shape of the magnet attachment face.

[0047] The rotor shaft can be made by stacking magnetic sheets. Stator

[0048] The stator may have concentrated winding. The stator may have teeth and coils arranged on the teeth. The stator may thus be wound on teeth, in other words with non-distributed winding. Alternatively, the stator could have distributed winding.

[0049] The stator teeth may have pole shoes. Alternatively, the stator teeth could be without pole shoes.

[0050] The opening of the stator slots, measured circumferentially, between the pole shoes where applicable, is for example between 0.175 mm and π*DS - N*LS mm (millimeters), where DS is the bore diameter of the stator, N the number of stator teeth, and LS is the width of the stator teeth, for example less than 8 mm, in particular between 0.5 and 3 mm, being for example of the order of 1.5 mm.

[0051] The stator teeth have end faces directed towards the rotor of concave shape, in the case of an inner rotor. Alternatively, in the case of an outer rotor, the stator teeth may have end faces directed towards the rotor of convex shape.

[0052] The end faces of the stator teeth may be, for example, portions of a cylinder, which may have a radius of curvature corresponding to the distance separating the top of the teeth from the axis of rotation X of the machine.

[0053] The bore DS of the stator, which corresponds to the internal diameter of the stator in the case of an external stator, is for example between 20 and 220 mm, better between 25 and 110 mm, being for example of the order of 70 mm.

[0054] The stator teeth form a stator yoke which may be a single piece, or alternatively may be formed from a string of teeth connected together by bridges of material, or from a plurality of separate teeth. In all cases, the stator may comprise an outer casing surrounding the yoke.

[0055] The stator teeth can be made with a stack of magnetic sheets, each covered with an insulating varnish, in order to limit losses by induced current. Machine

[0056] The machine can be a generator or a motor.

[0057] The rotating electrical machine according to the invention may have an external diameter for example between 40 and 280 mm, better between 50 and 220 mm, being for example of the order of 135 mm. The diameter may for example be less than or equal to 240 mm, being in particular between 40 mm and 190 mm.

[0058] The power of the machine can be between 0.1 and 15 kW, for example around 0.75 kW, this value being in no way limiting.

[0059] The machine may comprise a single inner rotor or, alternatively, a single outer rotor, or alternatively an inner rotor and an outer rotor, arranged radially on either side of the stator and coupled in rotation.

[0060] The number of notches per pole and per phase can be whole or fractional.

[0061] The number of poles P on the rotor is for example between 4 and 40 and the number of teeth S on the stator is for example between 6 and 48.

[0062] The invention also relates to a robot comprising a rotating electrical machine as described above for its motorization. Detailed description

[0063] The invention may be better understood by reading the detailed description which follows, non-limiting examples of its implementation, and by examining the attached drawing, in which: there Figure 1 is a schematic and partial view of a rotating electrical machine according to the invention, the Figures 2a and 2b are respectively transverse and longitudinal sectional views of a permanent magnet of the machine of the Figure 1 , and the Figure 3 is a view analogous to the Figure 1 of a variant embodiment.

[0064] We represented at the Figure 1a rotating electrical machine 1 according to the invention, comprising an outer stator 10 and an inner rotor 20 comprising a shaft 21 and permanent magnets 22 arranged on the surface of the shaft 21.

[0065] The stator 10 is in the example described with concentrated winding. The stator 10 comprises teeth 11 each carrying an individual coil 12 arranged on the corresponding tooth. The coils 12 are electrically connected to each other so as to be supplied by a three-phase current.

[0066] The stator teeth have polar expansions 13. The opening o of the stator notches, measured circumferentially, between the polar expansions 13, is for example of the order of 1.5 mm.

[0067] The stator bore, which is the inner diameter of the stator, is around 90 mm.

[0068] The stator still has an outer casing surrounding the yoke, not shown.

[0069] At the rotor, the shaft 21 is solid, being hollow in its middle, providing a space 26.

[0070] According to the invention, the permanent magnets 22 of the rotor have a face 23 directed towards the stator, which is of generally concave shape. The face 23 of the magnets directed towards the stator corresponds to the face of the magnets opposite the axis of rotation X of the machine.

[0071] The concave face 23 of a permanent magnet 22 of the rotor comprises a concave portion 24.

[0072] The width l of the concave portion 24, measured perpendicular to a radius of the rotor, in section, is of the order of 9 mm, in the example described.

[0073] The width L of a permanent magnet 22 of the rotor measured perpendicular to the axis of rotation, in section, is of the order of 13 mm.

[0074] The greatest depth pthe concavity of the concave portion, measured along a radius of the rotor, in section, is of the order of 0.5 mm.

[0075] The greatest depth of the concavity of the concave portion, measured along a radius of the rotor, is in the example described located in the middle of the concave face of the corresponding permanent magnet. The permanent magnet is symmetrical with respect to a plane P cutting it in its middle, this plane passing through the axis of rotation of the machine and a radius of the rotor.

[0076] The concave portion 24 is in the example described in section a portion of a circle, with radius R of the order of 20 mm.

[0077] The concave portion 24 of the concave face 23 is arranged between two flat lateral portions 26.

[0078] The width e of a flat lateral portion measured perpendicular to a radius of the rotor, in section, is of the order of 2 mm.

[0079] The concave portion constitutes in the example described approximately 75% of the total width of the corresponding magnet.

[0080] The permanent magnets of the rotor present, when the machine is observed along the axis of rotation, a generally rectangular cross-section, with the long side oriented perpendicular to a radius of the machine.

[0081] The permanent magnets 22 of the rotor have a thickness h, measured according to a radius of the rotor, in section, of the order of 3 mm.

[0082] A ratio p / h between the greatest depth p of the concavity of the concave portion, measured along a radius of the rotor, and the thickness h of the permanent magnet 22 is of the order of 0.2.

[0083] The rotor and the stator provide an air gap 30 between them. The air gap has a width, measured along a radius of the machine, in section, of the order of 0.9 mm. The width d 0 of the air gap, measured along a radius passing through the middle of a magnet 22, in section, is of the order of 1.5 mm.

[0084] The rotor bore, which is the outer diameter of the rotor, is around 50 mm.

[0085] The permanent magnets 22 of the rotor have a fixing face 28 opposite the concave face 23 directed towards the stator, which in the example described is of planar shape. The planar face is oriented perpendicular to the radius passing through the axis of rotation and intersecting the corresponding magnet 22 at mid-length.

[0086] The permanent magnets 22 are fixed to the rotor shaft by gluing in a housing 29 provided for this purpose on the surface of the shaft 21. The housing 29 has a flat surface corresponding to the shape of the fixing face of the magnets.

[0087] The concave face 23 may comprise one or more concave portions 24 and one or more flat portions 26, as illustrated previously, or be entirely concave, as illustrated by way of example in Figure 3 .

[0088] In this example, in the absence of a flat lateral portion, the concave portion 24 constitutes 100% of the total width of the corresponding magnet.

[0089] In the examples considered, the rotor has 16 poles and the stator has 18 teeth. It is not outside the scope of the present invention if their number is different.

[0090] The invention is not limited to the embodiments which have just been described, and the rotor may for example have a different number of poles, as may the teeth of the stator.

[0091] Furthermore, in the example described, the rotor is internal, but it does not go beyond the scope of the present invention if the rotor is external, or if the machine comprises both an internal rotor and an external rotor, each arranged radially on either side of the stator and coupled in rotation.

[0092] The machine can be used not only as a motor but also as a generator, to perform energy recovery, for example.

[0093] The machine according to the invention can find applications other than the motorization of robots.

Claims

1. Rotary electrical machine (1), comprising: - a stator (10), comprising teeth (11), and - a rotor (20), comprising a shaft (21) and permanent magnets (22) arranged on the surface of the shaft, the permanent magnets (22) comprising a face of concave overall shape directed towards the stator, a concave face (23) of a permanent magnet of the rotor comprises a concave portion (24), the concave portion (24) of a concave face being arranged between two planar lateral portions (26), the magnets having, when the machine is viewed along the axis of rotation, a cross section of elongate shape, the rotor being internal, the machine being characterized in that the width (1) of the concave portion, measured perpendicular to a radius of the rotor, is between 0.1π(DS-2d) / P and 2π(DS-2d) / P mm (millimetres), where DS is the bore diameter of the stator, P is the number of poles of the rotor, and d is the simple air gap, i.e. the smallest width of the air gap, the teeth of the stator having end faces of concave shape directed towards the rotor.

2. Machine according to the preceding claim, wherein a concave face (23) of a permanent magnet of the rotor comprises a concave portion (24) having a width (1), measured perpendicular to a radius of the rotor, of between 2 and 56 mm, better still between 8 and 12 mm.

3. Machine according to the preceding claim, the greatest depth (p) of the concavity of the concave portion, measured along a radius of the rotor, is between 0.05 and 3 mm, better still between 0.1 and 1.5 mm.

4. Machine according to either of the two preceding claims, the concave portion being a portion of a circle or ellipse in section.

5. Machine according to any one of the preceding claims, the permanent magnets of the rotor having a thickness (h), measured along a radius of the rotor, of between 2 and 10 mm, better still between 3 and 5 mm.

6. Machine according to any one of the preceding claims, a ratio (p / h) between the greatest depth of the concavity of the concave portion, measured along a radius of the rotor, and the thickness of a permanent magnet being between 0 and 0.9, better still between 0.1 and 0.4.

7. Machine according to any one of the preceding claims, the rotor and the stator forming an air gap (30) between them, the air gap having a width, measured along a radius of the machine, of between 0.5 and 3 mm, better still between 0.6 and 1.4 mm.

8. Machine according to the preceding claim, the width (d0) of the air gap measured along a radius passing through the centre of a magnet is between 0.5 and 5 mm, better still between 0.75 and 3 mm.

9. Machine according to any one of the preceding claims, the permanent magnets being fastened to the shaft of the rotor by adhesive bonding, in particular on a cylindrical surface of the shaft or in a housing (29) provided for this purpose on the surface of the shaft.

10. Machine according to any one of the preceding claims, the permanent magnets comprising a planar fastening face (28) on the opposite side to the concave face directed towards the stator.

11. Machine according to any one of the preceding claims, the stator (10) having concentrated winding, comprising coils (12) arranged on the teeth.

12. Machine according to the preceding claim, the teeth of the stator comprising pole shoes (13).

13. Machine according to the preceding claim, the opening (o) of the slots in the stator, measured circumferentially, between the pole shoes (13) if appropriate, is between 0.175 and 8 mm, better still between 0.5 and 3 mm.