ROTOR OF ELECTRIC MOTOR

Abstract

A rotor of electric motor is described comprising: a disc with a major surface and a rotation axis (X), the major surface of the disc comprising a circular recess in which a circular band or ring of material is arranged, the material being capable of magnetizing itself under the action of a magnetizing magnetic field, and internally partitioned into areas electrically isolated from one another, a circular series of permanent magnets arranged about the rotation axis (X) and resting on the circular band, a grid fixed to the disc for maintaining the position of the magnets on the disc.

Claims

1. Rotor of electric motor, comprising: a disc with a major surface and a rotation axis the major surface of the disc comprising a circular recess in which a circular band or ring of material is arranged, the material being capable of magnetizing itself under the action of a magnetizing magnetic field, and internally partitioned into areas electrically isolated from one another, a circular series of permanent magnets arranged about the rotation axis and resting on the circular band, a grid fixed to the disc for maintaining the position of the magnets on the disc.

2. Rotor according to claim 1, wherein said internally partitioned material consists of—or comprises—metallic laminations electrically insulated from one another.

3. Rotor according to claim 1, wherein said internally partitioned material consists of—or comprises—granules or powders electrically insulated from one another by an insulating coating.

4. Rotor according to claim 1, wherein said circular series of permanent magnets is formed by magnets in the form of an isosceles trapezium, with the larger base facing the periphery of the disc and the smaller base facing the center of the disc.

5. Rotor according to claim 1, wherein the grid comprises a ring equipped with a circular series of pass-through windows, each configured to receive a magnet and hold it on the disc.

6. Rotor according to claim 5, wherein each window and each magnet are configured so that their perimeter can be overlapped via shape-fitting.

7. Rotor according to claim 6, wherein the perimeter of each window comprises an inclined plane complementary to an inclined plane of a magnet.

8. Rotor according to claim 1, wherein the grid comprises interlocking and/or snap-in elements to be fixed to the disc.

9. Rotor according to claim 8, wherein the grid comprises a circular series of tabs projecting from its periphery and extending parallel to the rotation axis to fit into corresponding slots of a circular series of slots obtained on the periphery of the disc.

10. Rotor according to claim 9, wherein the tabs comprise a protruding tooth which can be fitted into a corresponding cavity of one of said slots.

11. Rotor according to claim 2, wherein said internally partitioned material consists of—or comprises—granules or powders electrically insulated from one another by an insulating coating.

12. Rotor according to claim 3, wherein said circular series of permanent magnets is formed by magnets in the form of an isosceles trapezium, with the larger base facing the periphery of the disc and the smaller base facing the center of the disc.

13. Rotor according to claim 4, wherein said circular series of permanent magnets is formed by magnets in the form of an isosceles trapezium, with the larger base facing the periphery of the disc and the smaller base facing the center of the disc.

Description

[0036] Further advantages will be clear from the following description, which refers to an example of a preferred embodiment of motor in which:

[0037] FIG. 1 shows a plan view of a rotor;

[0038] FIG. 2 shows a cross-sectional view of the rotor according to plane II-II.

[0039] FIG. 3 shows an exploded three-dimensional view of the rotor.

[0040] Equal numbers in the figures indicate equal or substantially equal parts; and in order not to crowd the drawings not all equal components are numbered.

[0041] With reference to FIG. 1, a rotor MC comprises a support disc 12 which is rotatable about a rotation and symmetry axis X.

[0042] The disc 12, e.g. made of aluminium, comprises a major surface 14 comprising a circular recess 16 in which there is arranged a circular band 30 made of material which is internally partitioned into electrically isolated areas. This material may be, for example, a set of metal laminations covered with an insulating layer or paint. For example, the laminations are rings all concentric to the axis X or a spiral concentric to the axis X or laminations arranged radially with respect to a center on the axis S. Or the material may be an agglomerate of granules covered by an insulating layer or paint, e.g. Somaloy.

[0043] In the band 30 permanent magnets 50 are placed in a circular series around the axis X. Windings of a stator (not shown) generate magnetic forces that act on the magnets 50 and make the rotor MC rotate.

[0044] The magnets 50 preferably have the shape of a flat plate in the shape of an isosceles trapezium, which lies in a plane orthogonal to the axis X and has the larger base facing the periphery of disc 12 and the smaller base facing the center of the disc 12. In this manner, the covering surface of the magnets 50 in the rotor MC increases. However, other shapes are possible.

[0045] In particular, the magnets 50 generate a magnetic field with a polar axis parallel to the axis X.

[0046] A perforated grid 60, e.g. made of plastic, is fixed to the disc 12 to maintain the position of magnets 50 on the disc 12.

[0047] The grid 60 comprises a ring 62 equipped with a circular series of pass-through windows 64 aligned with the recess 16.

[0048] The pass-through windows 64 and the magnets 50 have complementary-shaped edges, in particular edges with matching inclined planes, which can overlap to fix the magnets 50 on the band 14.

[0049] The grid 60 is fixed to the center of the disc 10 by screws 70 and to the periphery of the disc 12 by a circular series of tabs 66.

[0050] The tabs 66 protrude from the periphery of the ring 62 parallel to the axis X and can be snapped into a corresponding circular series of slots 18 made in the periphery of the disc 12, e.g. made in a raised edge of the disc 12. Preferably a or each tab 66 comprises a protruding end tooth 68 for the attachment inside a slot 18.

[0051] The band 30 assures to the magnetic field of the magnets 50 a controlled, high-magnetic-permeability closure path, thereby avoiding or limiting the leakage flux and therefore the amount of eddy currents.