Description AN ELECTRIC MOTOR

[0001] The present invention relates to a line start permanent magnet motor that operates asynchronously at the start-up and synchronously after start up.

[0002] Particularly in implementations wherein high start up moment and high operational efficiency is important, for example in compressors of cooling devices, hybrid type electric motors having asynchronous motor properties at the start, and synchronous motor features in continuous operation are utilized. Hybrid type electric motors are generally called "line start permanent magnet motor". In the rotor of the hybrid type electric motor, in addition to the structure of magnetic cage (squirrel cage) formed rotor bars having conductive and easily-shaped properties such as aluminum in the rotor slots and the end-rings that mechanically and electrically join these rotor bar ends on both surfaces of the rotor, permanent magnets are utilized that are emplaced inside the rotor. The hybrid motor starts asynchronously by means of the magnetic cage at the rotor and operates synchronously after start up by means of the permanent magnets placed in the rotor. The problem that arises in producing this type of rotors is reaching high temperatures while injecting aluminum material into the rotor slots and the magnets embedded in the rotor losing their magnetic properties due to high temperatures. In order to solve this problem, the magnets can be placed in the rotor after the aluminum injection process however another problem, the displacement of the magnets placed later on, is encountered. In order to place the magnets after the injection process, the shape of particularly the end ring is changed depending on the arrangement of the magnets and the shape variations in the end rings results in magnetic flux irregularities and disruptions in the rotor balance.

[0003] In the European patent application no. EP1519471, a permanent magnet synchronous motor is described which comprises a stator, a rotor and permanent magnets. The rotor comprises a rotor iron core, a plurality of conductor bars accommodated within corresponding slots in the rotor iron core and a starter squirrel cage conductor formed of a plurality of short-circuit rings positioned at axially opposite ends of the rotor iron core. Furthermore, the rotor includes magnet retaining slots on the inner sides of the conductor bars close to the periphery of the rotor and the permanent magnets are placed in these slots. End plates made of a non-magnetizable material is positioned between one or two laces of the rotor so as to prevent dislocation of magnets during operation. Shaping the short circuit rings depending on the magnet arrangement and

making the cross-section thinner at some places results in the increase of electrical resistance and balance problems arise. Furthermore, a separate path opened in the rotor core is to inject the aluminum that acts as a rivet in order to fix the end plates.

[0004] In the United States of America patent application no. US2004256939, the rotor of a line start permanent magnet motor and a manufacturing method thereof is described. A supporting plate is not used for preventing displacement of magnets embedded in the rotor during operation but instead the end ring is formed to cover the magnet slots and a third end ring is provided with magnet paths sized for respectively passing through the permanent magnets. After the injection process of end rings and the conductor bars on the rotor core is completed, the magnets are passed through the magnet paths to be embedded in the rotor core and afterwards the fixing members are mounted into the magnet paths of the third end ring for preventing the magnets from being separated. The magnet paths make the production of end rings more difficult and provide a barrier for the magnetic flux.

[0005] The aim of the present invention is the realization of a line start permanent magnet motor of which the start-up and operational efficiency is enhanced, comprising a low cost rotor with a simplified manufacturing process.

[0006] The electric motor realized in order to attain the aim of the present invention is explicated in the attached claims.

[0007] In the electric motor of the present invention, a magnet retaining ring is used to prevent the scattering of the displaced magnets emplaced in the rotor core after the aluminum injection process during high speed operation. The magnet retaining ring is produced separately from the end ring of the rotor on the side of the emplaced magnets, and after the magnets are placed in the magnet inserting holes, is passed into the end ring and seated on the circular surface of the rotor core on the side wherein the magnets are disposed. The magnet retaining ring contacts peripherally the inner side of the end ring formerly shaped by aluminum injection and covers the magnet inserting holes partially or entirely.

[0008] The end ring on the side of the emplaced magnets in the rotor and the magnet retaining ring form two rings, one inside the other, and the magnet retaining ring acts as the inner ring of the end ring and sharing the electrical load.

[0009] The magnet retaining ring can be fixed inside the end ring by press fitting, screwing or supported by fixing pins, electrically conductive adhesive is applied on the contact surfaces of the end ring and the magnet retaining ring to provide fixing and electrical conductivity is enhanced.

[0010] In the embodiment wherein the magnet retaining ring is fixed to the rotor by means of the fixing pin, the fixing pin is inserted into the pin housings arranged oppositely on the outer side of the magnet retaining ring and the inner side of the second end ring. The fixing pin, when pressed or hammered into the pin housing, pushes the second end ring outwards in the radial direction and the magnet retaining ring inwards providing these elements to be contracted and the assembly to be reinforced.

[0011] The lower end of the fixing pin, when inserted into the pin housing, bears on the rotor plate at the second circular surface, not going into the rotor lamination, hence a configuration that deforms the structure of the rotor laminates in the core is not required for attaching the fixing pin.

[0012] The upper end of the fixing pin, when inserted into the pin housing, projects a little bit outside the magnet retaining ring and the second end ring and after the assembly this projected end is flattened providing riveting of the fixing pin.

[0013] The magnet retaining ring can be produced in different sizes owing to the simple shape and can easily be adapted to different rotor and end ring designs. The magnet retaining ring prevents the displacement of magnets and the circular configuration thereof enhances the rotor balance. The magnet retaining ring, joining with the end ring, increases the total area for transmission of the generated flux, decreases electrical resistance and thus has a positive effect on performance.

[0014] The electric motor of the present invention is used in implementations wherein startup moment and operational efficiency is important such as compressors of cooling devices.

[0015] The electric motor realized in order to attain the aim of the present invention is illustrated in the attached figures, where:

[0016] Figure 1 - is the schematic view of an electric motor.

[0017] Figure 2 - is the perspective view of a rotor core.

[0018] Figure 3 - is the perspective view of a state of the art rotor core and a squirrel cage structure formed of end rings and conductor bars.

[0019] Figure 4 - is the perspective view of a rotor, the magnets to be disposed in the rotor and a magnet retaining ring.

[0020] Figure 5 - is the perspective view of a rotor before the magnet retaining ring is mounted.

[0021] Figure 6 - is the perspective view of a rotor after the magnet retaining ring is mounted.

[0022] The elements illustrated in the figures are numbered as follows:

1. Electric motor

2. Stator

3. Rotor

4. Core

5. Magnet

6. Magnet inserting hole

7. Rotor slot

8 Conductor bar

9. First circular surface

10. , 110. End ring

11. Second circular surface

12. Magnet retaining ring

13. Fixing pin

14. Pin housing

[0023] The line start permanent magnet motor (1) comprises a stator (2) and a rotor (3).

[0024] The rotor (3) comprises a core (4) of cylindrical configuration formed of magnetic steel rotor laminations (L) slacked on top of each other with a shaft hole (D) at the center, one or more magnets (5) disposed by being embedded into the core (4) in the axial direction, providing synchronous operation, one or more magnet inserting holes (6) around the periphery of the shaft hole (D) wherein the magnets (5) are embedded, more than one rotor slots (7) inside the core (4) at a region near the outer periphery thereof, in the axial direction and in the same direction as the shaft hole (D) axis or extending along the core (4) in a sloped manner with respect to the shaft hole (D) axis, more than one conductor bars (8) formed by injecting aluminum into the rotor slots (7) in the injection mould (K), a first circular surface (9) situated at the aluminum injected side of the core (4), a first end ring (10) formed on the first circular surface (9) at the mould (K) together with the conductor bars (8) by injecting on the core (4) and providing the connection of the conductor bars (8) at the first circular surface (9), a second circular surface (11) situated at the side wherein the injected aluminum goes out of the core (4) and a second end ring (110) formed on the second circular surface (11) in the mould (K), providing the connection of the conductor bars (8) at the second circular surface (11).

[0025] The conductor bars (8) injected into the rotor slots (7) together with the first and second end rings (10, 110) form the known magnetic squirrel cage structure (Figure 3).

[0026] During the production of the rotor (3) the core (4) is formed by stacking the rotor

laminations (L) on top of each other, with the shaft hole (D), rotor slots (7) and magnet inserting holes (6) provided thereon and aluminum is injected from the first circular surface (9) by emplacing the core (4) in the aluminum injection mould (K). While aluminum is injected into the core (4) from the first circular surface (9), the penetration of aluminum material into the magnet inserting holes (6) and the shaft hole (D) is prevented by various methods. The magnets (5) are arranged in the magnet inserting holes (6) after the aluminum injection process and thus the magnets (5) are prevented from being affected by high temperatures.

[0027] The rotor (3) of the present invention comprises a magnet retaining ring (12) produced separately from the second end ring (110), fitted on the second circular surface (11) of the core (4) by being inserted into the second end ring (110) after the magnets (5) are arranged in the magnet inserting holes (6), that contacts the inner side of the second end ring (110) peripherally and prevents the displacement of the magnets (5) by partially or entirely covering the magnet inserting holes (6) at the second circular surface (11) (Figures 4, 5).

[0028] In the rotor (3) of the present invention, the second end ring (110) does not have the dimensions to cover the magnet inserting holes (6). The inner diameter of the second end ring (110), the open portion thereof above the magnet inserting holes (6) being preferably circular, is dimensioned such that can it can pass from the outside of the magnet inserting holes (6).

[0029] The magnet retaining ring (12), while preventing the displacement of the magnets (5) from the magnet inserting holes (6), and also being in full contact with the inner wall of the second end ring (110), shares the electrical load and decreases the resistance of the second end ring (110) which is made thinner for arrangement of magnets (5) after the injection by increasing the inner diameter thus increasing the electrical resistance. Furthermore, the circular shape of the second end ring (110) prevents the problem of balance during high speed operation.

[0030] During the production of the rotor (3) of the present invention, the core (4) is formed by stacking the rotor laminations (L) on top of each other, with the shaft hole (D), rotor slots (7) and magnet inserting holes (6) provided thereon and aluminum is injected from the first circular surface (9). Firstly, the first end ring (10) is formed on the first circular surface (9) with the injected aluminum, afterwards the aluminum is allowed to flow through the rotor slots (7) thus forming the conductor bars (8). The aluminum injected into the core (5) goes out from the rotor slots (7) on the rotor lamination (L) at the second circular surface (11), forming the second end ring (110). After the injection

process, the magnets (5) are arranged in the magnet inserting holes (6). After the magnets (5) are arranged, the magnet inserting holes (6) are covered from above by the magnet retaining ring (12) that is mounted by being in full contact with the inner wall of the second end ring (110) and the displacement of the magnets (5) is prevented.

[0031] In an embodiment of the present invention, the magnet retaining ring (12) is fitted inside the second end ring (110) by press-fitting.

[0032] In another embodiment of the present invention, the rotor (3) comprises one or more fixing pins (13) that are disposed between the magnet retaining ring (12) and the second end ring (110) for fixing the magnet retaining ring (12) (Figures 4,5,6).

[0033] In this embodiment, the rotor (3) comprises more than one pin housing (14), preferably shaped as half-cylindrical dents between which the fixing pin (13) is fitted, situated oppositely on the outer side of the magnet retaining ring (12) and the inner side of the second end ring (110) (Figures 4, 5).

[0034] When the fixing pin (13) is fitted into the pin housing (14), it pushes the second end ring (110) radially outwards and the magnet retaining ring (12) inwards causing contraction and prevents the dislocation of the magnet retaining ring (12).

[0035] The length of the pin housing (14) equals the thickness of the magnet retaining ring

(12) and the second end ring (110), does not puncture in to the rotor lamination (L) at the second circular surface (11), when the fixing pin (13) is inserted into the pin housing (14) the lower end thereof bears on the rotor lamination (L) at the second circular surface (11). The fixing pin (13) presses on the magnet retaining ring (12) and the second end ring (110) by pushing inwards and outwards respectively and a configuration that deforms the structure of the rotor laminates (L) in the core (4) is not required for attaching the fixing pin (13).

[0036] The upper end of the fixing pin (13), when inserted into the pin housing (14), projects a little bit out of the magnet retaining ring (12) and the second end ring (110), this projected end is flattened after the assembly, providing riveting of the fixing pin

(13) (Figure 6).

[0037] In another embodiment of the present invention, screw threads and grooves are provided on the outer side of the magnet retaining ring (12) and the inner side of the second end ring (110), and the magnet retaining ring (12) is fitted inside the second end ring (110) by screwing.

[0038] In another embodiment of the present invention, an electrically conductive adhesive is applied on the outer side of the magnet retaining ring (12) and inner side of the second end ring (110), thus enhancing electrical conductivity therebetween as well as

fixing the magnet retaining ring (12) to the second end ring (110). The magnet retaining ring (12) can be produced easily due to the simple ring structure thereof and be conveniently adapted to different rotor (3) and end ring (10, 110) designs. The magnet retaining ring (12) prevents the displacement of magnets and the circular configuration thereof enhances the rotor (3) balance. The magnet retaining ring (12), joining with the second end ring (110), increases the total area for transmission of the generated flux, decreases electrical resistance and thus has a positive effect on performance.