This application is a U.S. National Stage Application under 35 U.S.C. § 371 of PCT Application No. PCT/KR2018/002391, filed Feb. 27, 2018, which claims priority to Korean Patent Application No. 10-2017-0033334, filed Mar. 16, 2017, whose entire disclosures are hereby incorporated by reference.

BACKGROUND

1. Field

An electric motor having a permanent magnet and a compressor having an electric motor are disclosed herein.

2. Background

As is well known, an electric motor is an apparatus that converts electric energy into mechanical energy. Electric motors are classified into a direct current (DC) type, a single phase alternating current (AC) type, and a three-phase AC type depending on an electric power (or power) supply system.

Such an electric motor generally includes a stator, and a rotor disposed to be movable relative to the stator with a predetermined gap therebetween. A part of the rotor includes a rotor core having a rotational shaft, a plurality of conductor bars inserted into the rotor core in an axial direction, and an end ring shorting the conductor bars. Another part of the rotor includes a permanent magnet, and a rotor frame provided with a rotational shaft to support the permanent magnet.

However, in the related art electric motor having the permanent magnet, a magnetic body (a back yoke) is provided at the rear of the permanent magnet to form a flux path, which causes an increase in a mass of the rotor. Vibration and noise may be increased when the mass of the rotor is increased.

Further, when the mass of the rotor is increased, the inertia of the rotor is increased, which may make it difficult to start and stop the rotor. In addition, the magnetic body is formed of a high-priced magnetic steel sheet (or electromagnetic steel sheet or silicon steel sheet) having a high magnetic property, which may cause an increase in manufacturing costs.

On the other hand, a compressor includes a case, a compression unit provided inside of the case to compress a refrigerant, and an electric motor provided inside of the case to supply a drive force to the compression unit. The compression unit includes a cylinder, and a roller provided inside of the cylinder and connected to the rotational shaft of the electric motor to be rollable.

The electric motor includes a stator fixed to the inside of the case, and a rotor rotatably disposed in the stator around the rotational shaft. Bearings are provided on both sides of the cylinder along the axial direction of the cylinder so as to rotatably support the rotational shaft protruding at the both sides of the cylinder.

However, in the related art compressor, the rotor is provided with a rotor core made of a magnetic material and a permanent magnet coupled to the rotor core. This causes an increase in the mass of the rotor which results in increasing vibration and noise. Particularly, as one side of the rotor is supported by the bearings extending along the axial direction of the rotational shaft, abrasion of the bearings is greatly increased when the mass and the vibration are increased.

Therefore, embodiments disclosed herein are directed to providing an electric motor having a permanent magnet capable of reducing mass of a rotor and suppressing vibration and noise occurrence and/or a compressor including the same. In addition, embodiments disclosed herein are directed to providing an electric motor having a permanent magnet capable of easily changing a material, a shape and a size of a rotor frame supporting the permanent magnet and/or a compressor including the same.

Further, embodiments disclosed herein are directed to providing an electric motor having a permanent magnet capable of reducing mass of a rotor and easily manufacturing a rotor and/or a compressor including the same. Furthermore, embodiments disclosed herein are directed to providing an electric motor having a permanent magnet capable of suppressing vibration of a rotor to reduce wear of a bearing.

In order to achieve the objects as described above, embodiments disclosed herein provide an electric motor having a permanent magnet including a stator; and a rotor rotatably disposed and spaced a predetermined gap apart from the stator. The rotor may include a rotational shaft; a permanent magnet disposed concentrically with the rotating shaft; and a permanent magnet support means or support that supports the permanent magnet. The permanent magnet may have a cylindrical shape and be magnetized in polar anisotropy such that a magnetic field is formed on a surface of the permanent magnet facing the gap and a magnetic field is not formed on a surface of the permanent magnet opposite to the gap. Accordingly, as the permanent magnet support means does not have to form a flux path, the design of the permanent magnet support means may be free.

According to one embodiment, the permanent magnet support means may include a rotor frame provided between the rotational shaft and the permanent magnet. The permanent magnet may have a cylindrical shape, and the rotor frame does not form a flux path of the permanent magnet, and is formed so as to connect the rotational shaft and the permanent magnet.

According to one embodiment, the rotational shaft and the rotor frame are formed of different materials, respectively. According to one embodiment, the rotor frame is configured to be injection-molded around the rotational shaft.

According to one embodiment, the rotational shaft is configured to have a protrusion protruding outwardly or a groove recessed inwardly along a radial direction from an outer surface, and the rotor frame is configured to have an engaging portion engaging with the protrusion or the groove along a rotational direction. According to one embodiment, the protrusion or the groove is formed to be spaced apart along an axial direction, and the rotor frame is configured to be injection-molded at an outer surface of the protrusion or the groove.

According to one embodiment, the rotational shaft and the rotor frame are configured to be formed of the same material. According to one embodiment, the rotational shaft and the rotor frame are formed of the same material, and the rotor frame is formed integrally so as to protrude from the outer surface of the rotational shaft along the radial direction.

According to one embodiment, the rotor frame includes a hub provided with the rotational shaft therein, a cylindrical part or portion disposed concentrically with the hub at an outer side of the hub, and a connecting part or portion connecting the hub and the cylindrical part.

According to one embodiment, the permanent magnet is a sintered magnet, and an adhesive layer is provided between the permanent magnet and the rotor frame. According to one embodiment, the rotor frame is formed to have a reduced length as compared with the permanent magnet along the axial direction.

According to one embodiment, the permanent magnet is a bonded magnet, and the permanent magnet is configured to be injection-molded at an outer surface of the rotor frame.

According to another embodiment, a compressor may include a case; a compression unit provided inside of the case to compress fluid; and an electric motor provided inside of the case and having the permanent magnet providing driving force to the compression unit. According to one embodiment, the compression unit may include a cylinder forming a compression space; a roller connected to a rotational shaft of the electric motor having the permanent magnet and rotated inside of the cylinder; and a bearing provided at the cylinder to rotatably support the rotational shaft.

According to one embodiment, the rotational shaft includes a first shaft portion coupled to a rotor frame and a second shaft portion coupled to the roller. The first shaft portion and the second shaft portion may be configured to be coupled integrally to each other after the rotor frame and the roller are coupled.

As described above, according to one embodiment, a permanent magnet is magnetized in polar anisotropy such that a magnetic field is formed on a surface of the permanent magnet facing a gap and a magnetic field is not formed on a surface of the permanent magnet opposite to the gap, and a permanent magnet support means (rotor frame) does not form a flux path of the permanent magnet and is formed to connect the rotational shaft and the permanent magnet, and thus, mass of a rotor may be reduced, and vibration and noise occurrence of the rotor may be suppressed.

Further, as the rotor frame supporting the permanent magnet may be formed independently of the formation of the flux path of the permanent magnet, a material, a shape, and a size of the rotor frame may be changed easily. Accordingly, not only the mass of the rotor may be reduced but also the rotor may be manufactured easily.

Further, as the rotor frame does not form the flux path, it may be formed integrally with the rotational shaft with the same material as that of the rotational shaft, thereby easily manufacturing the rotor. Furthermore, as the rotor frame does not form the flux path, the rotor frame is formed with a plastic which is a non-magnetic material and has a small gravity, thereby reducing the mass of the rotor.

In addition, as the rotor frame does not form the flux path, the rotor frame is injection-molded integrally at an outer surface of the rotational shaft, thereby easily manufacturing the rotor. Further, the rotor frame is injection-molded around the rotational shaft, and the permanent magnet is injection-molded around the rotor frame, thereby reducing the mass of the rotor and easily manufacturing the rotor.

Furthermore, the mass of the rotor is reduced and generation of vibration is suppressed, and thus, a compression unit is connected to one end portion of the rotational shaft of the rotor, and wear of a bearing provided between the rotor and the compression unit may be reduced remarkably. In addition, as the rotor frame is formed to be shortened in an axial direction as compared with the permanent magnet, and a bearing insert portion for inserting the bearing inside the rotor is not formed separately, the rotor may be easily manufactured.

