Device for magnetizing a ring-shaped magnet for a brushless DC motor

Abstract

Apparatus for magnetizing an annular magnet for a brushless direct current (BLDC) motor, comprising: a rotor (100) having an annular magnet (200) mounted on an outer peripheral surface of a rotor core (120); and a plurality of magnetizing yokes (300) arranged to be spaced apart from each other at a predetermined distance while facing an outer peripheral surface of the annular magnet (200), magnetizing the annular magnet (200) to form even-numbered unit magnets (210), and magnetizing the annular magnet (200) only in regions except one end and the other end of the unit magnets (210), characterized by that the magnetizing yoke (300) has a roughness formed on an inner peripheral surface thereof.

Description

TECHNICAL FIELDThe present disclosure relates to an apparatus for magnetizing an annular magnet for a brushless direct current (BLDC) motor.BACKGROUNDA direct current (BLDC) brushless motor is generally divided into a core type BLDC motor (or radial gap type BLDC motor) having a pot structure (cylindrical structure) and a coreless type BLDC motor (or axial gap type BLDC motor), depending on whether a stator core is present or not.The core-type BLDC motor is divided into an inner ring-type BLDC motor including a cylindrical stator having a coil wound around it to have a complete ring-type magnetic structure at a plurality of protrusions (teeth) formed on an inner peripheral portion thereof and a rotor configured of a cylindrical ring-type permanent magnet, and an outer ring-type BLDC motor including a stator having a coil wound around a plurality of protrusions (teeth) formed on an outer peripheral portion thereof in a vertical direction and a rotor configured of a cylindrical ring-type permanent magnet multipolarly magnetized at an outer portion thereof.Since the core-type BLDC motor includes a magnetic circuit having a symmetrical structure in a radial direction based on a shaft, the core-type BLDC motor has low axial vibration noise, is suitable for low-speed rotation, and has a very small portion occupied by an air gap in a direction of a magnetic path. Therefore, even when an annular magnet having a low power is used or a volume of the annular magnet is reduced, a high magnetic flux density can be obtained so that a torque is large and an efficiency is high.Meanwhile, the ring-shaped magnet installed in the BLDC motor is subjected to a magnetization process to drive the motor and generate a frequency.FIG. 1 is a schematic view of an apparatus for magnetizing a ring-shaped magnet for a BLDC motor according to the related art.As shown in FIG. 1, the annular magnet magnetizing apparatus for a BLDC motor according to the related art is configured to include a rotor 10 including a rotor core 12 having a shaft 11 inserted therein and an annular magnet 20 mounted on an outer circumferential surface of the rotor core; and a plurality of magnetizing yokes 30 mounted to face an outer circumferential surface of the annular magnet.Here, a magnetizing voltage is applied to the magnetizing yokes 30, so that a magnetic flux is generated by a magnetizing iron core, and even-numbered unit magnets 21 in the ring-shaped magnet 20 are magnetized by the magnetic flux.The even-numbered unit magnets 21 are connected to each other, so that one of them may have magnetism of an S pole and the other of them may have magnetism of an N pole.FIG. 2 is a graph illustrating magnetic flux densities of unit magnets formed by magnetizing the ring-shaped magnet for a BLDC motor according to the related art depending on an electrical degree.A portion shown by electrical degrees from 0 degrees to 180 degrees on the left of the graph of FIG. 2 is a graph showing a magnetic flux density of a unit magnet having magnetism of an N pole depending on an electrical degree, the electrical degrees from 0 degrees to 180 degrees in FIG. 2 denote portions from one end of the unit magnet having magnetism of the N pole to the other end thereof, and the electrical degrees from 180 degrees to 360 degrees denote portions from one end of a unit magnet having magnetism of an S pole to the other end thereof.Referring to FIG. 2, it can be confirmed that dead zones in which a magnetic flux density is rapidly changed are generated in one end and the other end of the unit magnet having the magnetism of the N pole and one end and the other end of the unit magnet having the magnetism of the S pole.Therefore, according to the prior art, there is a problem that a cogging phenomenon and a torque ripple phenomenon occur, which are rotation follow-up phenomena of the ring-shaped magnet due to a rapid change in magnetic resistance caused by the 'dead zones' of the even-numbered unit magnets constituting the ring-shaped magnet.Therefore, development of various apparatuses for magnetizing a ring-shaped magnet for a BLDC motor has been demanded for solving the above-mentioned problem.As a related technology, an apparatus for magnetizing a motor magnet has been disclosed in Korean Patent Laid-Open Publication No. KR 10 2000 0 044 134 A.Document EP 0 549 427 A1 shows a device for magnetizing an annular magnet according to the preamble of claim 1. Further prior art is known from the documents US 2005 / 0 076 973 A1 and US 7 560 841 B2.SUMMARYAn object of the present invention is to provide an annular magnet magnetizing apparatus for a brushless direct current (BLDC) motor that can minimize a cogging phenomenon and a torque ripple phenomenon, which are rotation tracking phenomena of the annular magnet, by reducing rapid changes in magnetic flux densities in one end and the other end of unit magnets constituting the annular magnet.In a general view, an apparatus for magnetizing an annular magnet for a BLDC motor includes: a rotor 100 including an annular magnet 200 mounted on an outer circumferential surface of a rotor core 120; and a plurality of magnetizing yokes 300 arranged to be at a predetermined distance from each other while facing an outer circumferential surface of the annular magnet 200, magnetizing the annular magnet 200 to form even-numbered unit magnets 210, and magnetizing the annular magnet only in regions except one end and the other end of the unit magnets 210.A magnetization angle of the magnetization yoke 300 for the unit magnet 210 may be 0.7 to 0.8 times the pole pitch of the unit magnet 210.An inner circumferential surface of the magnetizing yoke 300 may be formed in a shape corresponding to an inner circumferential surface of the unit magnet 210.The magnetizing yoke 300 has a roughness formed on an inner circumferential surface thereof according to the present invention.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a schematic view of a prior art apparatus for magnetizing a ring-shaped magnet for a brushless direct current (BLDC) motor. FIG. 2 is a graph illustrating magnetic flux densities of unit magnets formed by magnetizing the ring-shaped magnet for a BLDC motor according to the related art depending on an electrical degree. FIG. 3 is a schematic view of an apparatus for magnetizing an annular magnet for a BLDC motor according to an exemplary embodiment of the present invention. FIG. 4 is a graph illustrating magnetic flux densities of unit magnets formed by magnetizing the ring-shaped magnet for a BLDC motor according to the exemplary embodiment of the present invention depending on an electrical degree.[Detailed Description of Main Elements]100 Rotor 110 Shaft 120 Rotor core 200 Annular magnet 210 Unit magnet 300 Magnetizing yokeDETAILED DESCRIPTION OF EMBODIMENTSHereinafter, the technical spirit of the present invention will be described in more detail with reference to the accompanying drawings.The accompanying drawings are only examples shown to describe the technical idea of the present invention in more detail. Therefore, the technical idea of the present invention is not limited to forms of the accompanying drawings.FIG. 3 is a schematic view of an apparatus for magnetizing an annular magnet 200 for a brushless direct current (BLDC) motor according to an exemplary embodiment of the present invention.As shown in FIG. 3, the annular magnet magnetizing apparatus 200 for a BLDC motor according to the exemplary embodiment of the present invention is configured to include a rotor 100, an annular magnet 200, and magnetizing yokes 300.The rotor 100 is configured to include a shaft 110 and a rotor core 120.The shaft 10 is linked to a drive shaft (not shown) of the motor.The rotor core 120 is coupled to an outer circumferential surface of the shaft 110 and may be made of aluminum or plastic to minimize expansion due to thermal expansion.Further, rubber or silicone resin for absorbing noise may be coupled to an inner circumferential surface and an outer circumferential surface of the rotor core 120.The ring-shaped magnet 200 is mounted on the outer circumferential surface of the rotor core 120 and may be made of a ferromagnetic substance.The magnetizing yokes 300 are arranged so as to be spaced a predetermined distance from each other while facing an outer circumferential surface of the ring-shaped magnet 200, magnetizing the ring-shaped magnet 200 to form even-numbered unit magnets 210, and magnetizing the ring-shaped magnet 200 only in regions except for one end and the other end of the unit magnets 210.Here, rapid changes in the magnetic flux densities in one end and the other end of the unit magnets 210 are reduced, thereby making it possible to reduce the occurrence of a cogging phenomenon and a torque ripple phenomenon that are rotation tracking phenomena of the ring-shaped magnet 200 due to rapid changes in the magnetic resistances of the unit magnets 210 in the ring-shaped magnet 200.This will be described in more detail.FIG. 4 is a graph illustrating magnetic flux densities of unit magnets 210 formed by magnetizing the ring-shaped magnet 200 for a BLDC motor according to the exemplary embodiment of the present invention depending on an electrical degree. Electrical degrees from 0 degrees to 180 degrees in FIG. 4 denote portions from one end of the unit magnet 210 having magnetism of an N pole to the other end thereof, and electrical degrees from 180 degrees to 360 degrees denote portions from one end of the unit magnet 210 having magnetism of an S pole to the other end thereof.Referring to FIG. 4, in the unit magnet 210 for a BLDC motor formed by magnetizing the ring-shaped magnet 200, it can be confirmed that rapid changes in magnetic flux densities in one end and the other end of the unit magnet 210 having the magnetism of the N-pole and one end and the other end of the unit magnet 210 having the magnetism of the S-pole are reduced.Therefore, it can be confirmed that the rapid changes in the magnetic flux densities in one end and the other end of the unit magnets 210 are reduced, thereby making it possible to reduce the occurrence of the cogging phenomenon and the torque ripple phenomenon that are rotation hunting phenomena of the ring-shaped magnet 200 due to rapid changes in the magnetic resistances of the unit magnets 210 in the ring-shaped magnet 200.Further, it can be confirmed that magnetic flux densities from one end of the unit magnet having the magnetism of the N pole to the other end thereof and magnetic flux densities from one end of the unit magnet 210 having the magnetism of the S pole to the other end thereof are kept constant.Therefore, it can be confirmed that the magnetic flux densities from one end of the unit magnets 210 to the other end thereof are also kept constant, so that the magnetic resistances of the unit magnets 210 in the ring-shaped magnet 200 are kept constant, thereby making it possible to reduce the occurrence of the cogging phenomenon and the torque ripple phenomenon which are the revolution hunting phenomena of the ring-shaped magnet 200.Meanwhile, the magnetizing yoke 300 may be configured such that a magnetizing angle thereof for the unit magnet 210 is 0.7 to 0.8 times the pole pitch of the unit magnet 210.That is, only a region corresponding to 70 to 80% of the pole pitch of the unit magnet 210 is magnetized.An inner circumferential surface of the magnetizing yoke 300 may be further formed in a shape corresponding to an inner circumferential surface of the unit magnet 210.That is, only a portion of an entire range of the pole pitch of the unit magnet 210 is magnetized.The magnetizing yoke 300 may further have a roughness formed on the inner circumferential surface thereof.In the case where the roughness is formed on the inner circumferential surface of the magnetizing yoke 300, a strength at which the magnetizing yoke 300 magnetizing the ring-shaped magnet 200 is weakened to weaken a magnetic flux density of the unit magnet, thereby making it possible to alleviate the cogging phenomenon and the torque ripple phenomenon, which are the rotation hunting phenomena of the ring-shaped magnet.Therefore, the annular magnet magnetizing apparatus for a BLDC motor according to the exemplary embodiment of the present invention includes the plurality of magnetizing yokes that magnetize the annular magnet to form the even-numbered unit magnets and magnetize the annular magnet only in the regions except one end and the other end of the unit magnets to reduce the rapid changes in the magnetic flux densities in one end and the other end of the even-numbered unit magnets that form the annular magnet, thereby making it possible to minimize the cogging phenomenon and the torque ripple phenomenon that are the rotation tracking phenomena of the annular magnet.The present invention is not limited to the above-mentioned exemplary embodiments and can be variously applied and can be variously modified without departing from the spirit of the present invention claimed in the claims.

Claims

An apparatus for magnetizing an annular magnet for a brushless DC (BLDC) motor, comprising: a rotor (100) having an annular magnet (200) mounted on an outer circumferential surface of a rotor core (120); and a plurality of magnetizing yokes (300) arranged to be at a predetermined distance from each other while facing an outer circumferential surface of the annular magnet (200), magnetizing the annular magnet (200) to form even-numbered unit magnets (210), and magnetizing the annular magnet (200) only in regions except one end and the other end of the unit magnets (210), characterized in that the magnetizing yoke (300) has a roughness formed on an inner circumferential surface thereof.The apparatus for magnetizing an annular magnet for a BLDC motor according to claim 1, wherein a magnetizing angle of the magnetizing yoke (300) for the unit magnet (210) is 0.7 to 0.8 times the pole pitch of the unit magnet (210).The apparatus for magnetizing an annular magnet for a BLDC motor according to claim 1, wherein an inner circumferential surface of the magnetizing yoke (300) is formed in a shape corresponding to an inner circumferential surface of the unit magnet (210).

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