WO2011048581A2

WO2011048581A2 - An electric motor with a permanent-magnet rotor and a rotor for an electric motor of this type

Info

Publication number: WO2011048581A2
Application number: PCT/IB2010/054804
Authority: WO
Inventors: Lorenzo Giordanino; Christian Girardi
Original assignee: SICOR SpA; SICOR Societa Italiana Corticosteroidi SRL
Current assignee: SICOR SpA; SICOR Societa Italiana Corticosteroidi SRL
Priority date: 2009-10-22
Filing date: 2010-10-22
Publication date: 2011-04-28
Anticipated expiration: 2012-04-22
Also published as: ITBO20090688A1; WO2011048581A3; AR078725A1; IT1397689B1

Abstract

An electric motor for lifts and the like comprises a rotor (11) mounted so as to be rotatable relative to the stator (3) with a cylindrical wall facing the substantially cylindrical surface of the stator. Permanent magnets (21, 21') are fixed to the substantially cylindrical wall of the rotor (11) and are spaced from the substantially cylindrical surface of the rotor (11) by a gap. The permanent magnets (21, 21') are fixed to the substantially cylindrical wall of the rotor (11) by means of a form fit, for example, a dovetail joint, and are inserted in grooves (17, 17') formed integrally in the rotor body (11).

Description

AN ELECTRIC MOTOR WITH A PERMANENT-MAGNET ROTOR AND A ROTOR FOR AN ELECTRIC MOTOR OF THIS TYPE

The present invention relates to the field of electric motors .

The invention has been developed particularly but in non- limiting manner with regard to an electric motor with a permanent-magnet rotor for use, for example, for driving lifts and other mobile platforms such as, for example, hoists, elevators, and the like. The invention also relates to a rotor for an electric motor of this type.

Nowadays, the lifts that are mainly in use are substantially of two types: electric lifts and oleodynamic lifts. As far as electric lifts are concerned, they generally comprise at least the following elements: lifting machinery comprising an electric motor, a passenger cabin, a counterweight, hauling cables, an electric control panel, and safety devices comprising a speed limiter and a parachute. For the construction of electric lifts, it is possible to use electric motors of various types such as, for example, electric motors with reduction gearing comprising, for example, a pinion or a gear and a worm screw, or electric motors without reduction gearing, so-called "gearless" motors, in which the drum on which the hauling cables of the lift are wound is mounted directly on the drive shaft that is fixed to the rotor of the electric motor. The present invention relates to motors in which the rotor comprises a series of permanent magnets and interacts with a stator on which electrical windings are provided for generating the electric field which interacts with the permanent magnets of the rotor. In comparison with electric motors with gearing, so-called "gearless" electric motors offer various advantages including small size, low noise, low electrical energy consumption, greater flexibility of configuration, a complete absence of lubricating oil, and high levels of comfort and precision of movement. The above-mentioned small size feature of "gearless" electric motors in many cases allows the motor to be mounted directly in the lift shaft thus avoiding the need to provide a machine room for housing the motor. This latter type of lift which does not have a machine room is generally known by the name "roomless lift" and affords undoubted advantages in terms of cost and space savings.

The present invention relates in particular to an electric motor comprising a stator with electrical windings and a rotor with permanent magnets facing the stator.

It is known to fix the permanent magnets on the surface of the rotor by gluing. However, the operating conditions of the motor and, in particular, the vibrations, to which it is subjected in operation may cause the magnets to come unstuck with the serious consequence of complete stoppage of the motor and hence also of the lift.

An alternative solution provides for the permanent magnets to be held by a cage fixed to the rotor surface. This solution is more complex and expensive from the point of view both of the construction and of the assembly of the rotor.

In similar manner to the above-mentioned solution which provides for the use of a cage, other known solutions provide for the magnets to be held on the rotor surface by means of anchoring structures comprising ties, plates or other members of this type. Documents DE-10051308 and DE-10236609 show some of these known solutions which involve high costs and constructional complexity and do not fully ensure a perfect connection of the magnets to the rotor surface since vibrations may cause loosening of the anchoring structures and detachment of the magnets, with the above-mentioned serious consequences.

Another solution for the fixing of the permanent magnets to a rotor is described in EP-0734112 by Kone Corporation and provides for the injection of a filling material into cavities for housing the magnets. The filling material solidifies, forming an undercut abutment which prevents the permanent magnets from coming out of the respective housing cavities formed in the rotor. As well as being expensive and complex both in the production and in the assembly of the rotor, this solution leads to the disadvantage that the correct positioning and fixing of the magnets to the rotor depends mainly on the quality of the filling material, on its stability and strength over time, and on the correct procedure for its application and solidification.

Another solution of the type indicated above, in which the magnets are held on the rotor surface by a material which solidifies is described in document JP-9019091.

The objective of the present invention is to solve the problems of the prior art by providing an electric motor with a permanent-magnet rotor which is economical in production and reliable in use. A further objective of the present invention is to provide an electric motor of simple construction and assembly with a simple structure and a small number of components.

In order to achieve the objectives indicated above, the present invention relates to an electric motor and to a rotor for an electric motor of this type, as defined in the appended claims.

Further features and advantages will become clear from the detailed description of a preferred embodiment of the invention which follows, with reference to the appended drawings which are provided purely by way of non-limiting example, and in which:

Figure 1 is a side view of an electric motor according to the present invention;

Figure 2 is a view taken on the arrow F of Figure 1;

Figure 3 is a cross section through a stator of the electric motor shown in Figures 1 and 2;

Figure 4 is a cross section through a rotor of the electric motor shown in Figures 1 and 2;

Figure 5 shows a detail of the rotor shown in Figure 4, on an enlarged scale;

Figure 5b shows a variant of the detail shown in Figure 5, on an enlarged scale;

Figure 6 is a cross section through a permanent magnet of the electric motor shown in Figures 1 and 2;

Figure 6b is a cross section through a variant of the permanent magnet shown in Figure 6; and

Figure 7 is a perspective view of the connection of the permanent magnet of Figure 6 to the rotor of Figure 4. With reference now to Figures 1 and 2, a gearless electric motor, indicated 1, comprises a stator 3 inside which a rotor 11 can rotate about an axis X. As can best be seen in Figure 3, the stator 3 comprises a substantially circular ring- shaped outer casing 5 extending rectilinearly along the axis X . A series of radially-directed protuberances 7 of substantially uniform radial extent extend inwardly from an inner cylindrical surface of the outer casing 5 so as to give rise to a substantially cylindrical space 9 inside the stator 3. A series of electrical windings, which are not shown for simplicity of representation, are wound around the protuberances 7 of the stator 3 and are connected to an electrical supply circuit.

The electric motor 1 further comprises a rotor 11, shown in greater detail in Figure 4, which also has a substantially circular ring-shape extending rectilinearly along the axis X so as to define an outer surface 13 and an inner surface 15 both of substantially cylindrical shape, and the latter defining a space 16 in its interior. A series of grooves 17 are formed on the outer surface 13, preferably extending, as can best be seen in Figure 7, over the entire longitudinal dimension of the rotor 11 from one of the bases 11a, lib to the other base of the cylindrical rotor 11 so that each groove 17 has at least one opening 17a in one and preferably also in the other of the bases 11a, lib of the rotor 11. As shown in Figure 5, the grooves 17 have a substantially isosceles trapezoidal cross-section which becomes narrower towards the exterior of the rotor 11. Each groove 17 is thus limited laterally by two substantially flat abutment surfaces 19 which are defined on the rotor 11 and are inclined to the corresponding radial directions of the rotor. The rotor 11 may optionally be constructed integrally with the shaft 25 so as to afford greater robustness and reliability of the electric motor 1.

A permanent magnet 21 of the type shown in Figure 6 is inserted in each groove 17. The permanent magnet 21 has a shape that is substantially complementary to that of a groove 17 with a form fit, by way of non-limiting example, of the dovetail type. In greater detail, in the preferred but non- limiting embodiment shown in the drawings, the permanent magnet 21 has a cross-section generally comparable to an isosceles trapezium which is defined laterally by two oblique and preferably but in non-limiting manner, flat engagement surfaces 23 and, at the top, by a smaller base surface 24 which is preferably curved outwardly and will remain exposed after the fitting of the permanent magnet 21 in the groove 17. As is clear from Figure 7, when the permanent magnet 21 is fitted in a groove 17, its engagement surfaces 23 come into abutment with the corresponding abutment surfaces 19 of the rotor 11 so as to achieve a form fit which ensures a stable connection of the permanent magnet 21 to the rotor 11. Naturally, this form fit can advantageously also be achieved with grooves 17 and permanent magnets 21 having shapes other than those described above and illustrated in Figures 4, 5 and 6. For example, as shown in Figure 5b, a series of substantially "T"-shaped grooves 17 ' may be formed longitudinally in the outer surface 13 of the rotor 11 so as to define two abutment surfaces 19' arranged substantially tangentially with respect to the rotor 11. A permanent magnet 21' of the type illustrated in Figure 6b is inserted in each groove 17'. The permanent magnet 21' has a shape substantially complementary to that of the groove 17'; in particular, it has two engagement surfaces 23' corresponding to the arms of the "T", which come into abutment with the abutment surfaces 19' defined by the groove 17', and an outer surface 24' which is preferably curved outwardly and remains exposed after the fitting of the permanent magnet 21' in the groove 17¹.

The rotor 11 is arranged centrally in the space 9 of the stator 3, so that the permanent magnets 21 mounted on the rotor 11 face the protuberances 7 and the respective electrical windings and are spaced therefrom by a predetermined gap. The rotor 11 is also mounted firmly on a shaft 25 as shown in Figure 7.

The permanent magnets 21 may additionally be glued inside the respective grooves 17, as a precaution to prevent accidental longitudinal sliding of the magnets in the grooves because of vibrations of the motor in use.

According to a variant of the present invention, two or more aligned permanent magnets 21, 21' are inserted in each of the grooves 17, 17' formed in the outer surface 13 of the rotor 11. This latter configuration is particularly advantageous for the provision of magnets of a single length measurement which can be used in the manufacture of motors with rotors of multiple lengths (and hence powers) .

During the assembly of the rotor 11, the magnets 21 or 21' are fitted into the grooves 17, 17' by being inserted through the corresponding openings 17a, which emerge in one and/or the other of the bases 11a, lib of the rotor 11, and the magnets are then pushed in a longitudinal direction as shown clearly by the arrow A in Figure 7 until they reach the working position in which they do not project from the base 11a or lib of the rotor 11. Magnetic attraction and the form fit between the grooves and the magnets hold the magnets in position even in the presence of considerable vibrations when the motor comprising the rotor is in use. Optional gluing of the magnets to the surface of the rotor 11 eliminates any remaining doubt with regard to the fastness of the coupling.

The present invention may advantageously also be applied to so-called external-rotor electric motors, in which the rotor provided with permanent magnets is arranged outside the stator which is provided with electrical windings.

Naturally, the principle of the invention remaining the same, the forms of embodiment and details of construction may vary widely with respect to those described and illustrated, without thereby departing from the scope of the invention.

Claims

1. An electric motor for lifts and the like, comprising:

- a stator (3) with electrical windings arranged around a substantially cylindrical surface,

- a rotor (11) mounted so as to be rotatable relative to the stator (3) with a substantially cylindrical wall facing the substantially cylindrical surface of the stator,

- an array of permanent magnets (21, 21') which are fixed to the substantially cylindrical wall of the rotor (11) and are spaced from the substantially cylindrical surface of the stator (3) by a gap, characterized in that the array of permanent magnets (21, 21') is fixed to the substantially cylindrical wall of the rotor (11) by means of a form fit, the array of permanent magnets (21, 21') being housed in a corresponding plurality of cavities (17, 17') formed integrally in the body of the rotor ( 11 ) .

2. An electric motor according to Claim 1 wherein the cavities (17, 17') are formed longitudinally in the substantially cylindrical wall of the rotor (11) .

3. An electric motor according to Claim 2 wherein the cavities (17, 17') emerge with openings (17a) in at least one of the two bases (11a, lib) of the rotor (11) . . An electric motor according to Claim 3 wherein the permanent magnets (21, 21') are inserted through the openings (17a) in at least one of the bases (11a, lib) of the rotor (11) and are pushed longitudinally (A) into a working position in the corresponding cavities (17, 17').

5. An electric motor according to any one of the preceding claims wherein each cavity of the plurality of cavities (17, 17') comprises two abutment surfaces (19, 19') which are abutted by two respective engagement surfaces (23, 23') defined on each permanent magnet of the array of permanent magnets (21, 21'), said abutment surfaces (19, 19') holding the permanent magnet (21, 21') in the cavity (17, 17').

6. An electric motor according to Claim 5, characterized in that the abutment surfaces (19, 19') of the cavities (17, 17') and the engagement surfaces (23, 23') of the permanent magnets (21, 21') are inclined relative to the corresponding radial directions of the rotor (11) to achieve the form fit.

7. An electric motor according to any one of the preceding claims, characterized in that two or more longitudinally aligned permanent magnets (21, 21') are arranged in each cavity (17, 17 ' ) .

8. An electric motor according to any one of the preceding claims, characterized in that the array of permanent magnets (21, 21') is further fixed to the substantially cylindrical wall of the rotor (11) by gluing.

9. An electric motor according to any one of the preceding claims, characterized in that the motor comprises a drum for the winding of hauling cables for lifts and the like, which drum is coupled directly to the rotor (11).

10. An electric motor according to any one of the preceding claims, characterized in that the rotor (11) is arranged inside the stator (3).

11. An electric motor according to any one of Claims 1 to 9, characterized in that the rotor (11) is arranged outside the stator (3) .

12. A rotor for an electric motor for lifts and the like, comprising a substantially cylindrical wall, an array of permanent magnets (21, 21') being fixed to the substantially cylindrical wall of the rotor (11) by means of a form fit and being housed in a corresponding plurality of cavities (17, 17') formed integrally in the body of the rotor (11).

13. A rotor for an electric motor according to Claim 12 wherein the cavities (17, 17') are formed longitudinally in the substantially cylindrical wall of the rotor (11).

14. A rotor for an electric motor according to Claim 13 wherein the cavities (17, 17') emerge with openings (17a) in at least one of the two bases (11a, lib) of the rotor (11) .

15. A rotor for an electric motor according to Claim 14 wherein the permanent magnets (21, 21') are inserted through the openings (17a) in at least one of the bases (11a, lib) of the rotor (11) and are pushed longitudinally (A) into a working position in the corresponding cavities (17, 17').

16. A rotor for an electric motor according to any one of Claims 12 to 15 wherein each cavity of the plurality of cavities (17, 17') comprises two abutment surfaces (19, 19') which are abutted by two respective engagement surfaces (23, 23') defined on each permanent magnet of the array of permanent magnets (21, 21'), said abutment surfaces (19, 19') holding the permanent magnet (21, 21') in the cavity (17, 17 ' ) .

17. A rotor for an electric motor according to Claim 16, characterized in that the abutment surfaces (19, 19') of the cavities (17, 17') and the engagement surfaces (23, 23') of the permanent magnets (21, 21') are inclined relative to the corresponding radial directions of the rotor (11) to achieve the form fit.

18. A rotor for an electric motor according to any one of claims 12 to 17, characterized in that two or more longitudinally aligned permanent magnets (21, 21 ' ) are arranged in each cavity (17, 17').

19. A rotor for an electric motor according to any one of the preceding claims, characterized in that the array of permanent magnets (21, 21 ' ) is further fixed to the substantially cylindrical wall of the rotor (11) by gluing.

20. A rotor for an electric motor according to any one of Claims 12 to 19, characterized in that it comprises a drum for the winding of hauling cables for lifts and the like, which drum is coupled directly to the rotor (11).