KR20080048596A - Brushless motor of interior rotor type with decreased cogging torque - Google Patents

Abstract

An interior rotor type brushless motor with decreased cogging torque is provided to minimize non-uniformity of a magnetic force by dispersing magnetic flux through a through channel. An interior rotor type brushless motor includes a rotor(100), a plurality of permanent magnets(120), a stator(200), and a plurality of driving coils. The rotor is formed in a cylindrical shape. The permanent magnets are included inside the rotor and radially arranged at the same intervals. The stator is formed in a hollow cylindrical shape surrounding the rotor and includes a plurality of teeth(210) formed toward a center from an inner circumferential surface. The driving coils are wound around the teeth of the stator. The rotor includes a through channel(130) which is formed between an outer surface of the rotor and the permanent magnets along an axial direction.

Description

BRUSHLESS MOTOR OF INTERIOR ROTOR TYPE WITH DECREASED COGGING TORQUE}

1 is a cross-sectional view of an example of a general electric propulsion brushless motor,

2 is a graph showing a change in the size of the cogging torque according to the rotation angle of the rotor in the brushless motor of FIG.

3 is a cross-sectional view of one embodiment of a brushless motor according to the present invention;

4A and 4B are schematic views schematically showing magnetic flux around a through channel of the embodiment of FIG. 3;

5 is a graph illustrating a change in the size of the cogging torque according to the rotation angle of the rotor of the embodiment of FIG.

<Explanation of symbols for the main parts of the drawings>

100: rotor 110: rotating shaft ball

120: permanent magnet 130: through channel

200: stator 210: chi

220: yoke part

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless motor, and more particularly, to a brushless motor in which cogging torque is reduced in a permanent magnet embedded brushless motor.

The existing DC motor is required to improve the reliability, reduction in lifespan, and maintenance according to the switching drive caused by the mechanical contact between the commutator and the brush. Therefore, in recent years, it has been replaced by an electronic switching brushless motor (BLDC motor) using a semiconductor device. The brushless motor uses a switching method using a semiconductor element, which eliminates the need for mechanical contact, thereby providing a long service life of the motor, and using a permanent magnet having a high energy density, which is advantageous for high efficiency and miniaturization, and is easy to control shifts. The advantage is that the demand is increasing day by day. Brushless motors are classified into an interior rotor type and an exterior rotor type according to their structure, which are driven coils around an integrated rotor by attaching or bonding an axis to a cylindrical permanent magnet. The wound stator is arranged, and the abduction type motor has a structure in which a rotor with a permanent magnet is rotated around the stator in which the coil is wound, that is, a cup-shaped rotor surrounds the driving coil. Among these, the electric motor is particularly used for small motors and servo motors because of its low rotational inertia and easy balancing of rotors.

1 is a cross-sectional view showing an example of such a general electric type brushless motor. A general brushless motor has a rotor 10 having a plurality of permanent magnets radially with respect to a rotation axis of a central region, and a cylindrical stator having a plurality of teeth 21 and accommodating the rotor 10. It consists of 20.

Rotor 10 has a rotating shaft hole 12 is formed so that the rotating shaft (not shown) is inserted through, the plurality of permanent magnets 11 are arranged radially outward. As shown in FIG. 1, the permanent magnet 11 is embedded toward the center of the rotor 10 in a form in which a plurality of permanent magnets 11 are arranged in an outer circumferential surface of the rotor 10 as an arc to form an annular shape. The permanent magnet embedded motor is referred to as a permanent magnet embedded motor.

The stator 20 is provided with a plurality of teeth 21 protruding inward toward the rotor 10 and a drive coil wound thereon, and a yoke portion 22 for interconnecting each of these teeth. And a slot 23 is formed between the adjacent teeth.

The brushless motor having such a structure is the main driving characteristic that the accurate speed control is possible. For this purpose, it is necessary to reduce the torque ripple, which is the main cause of worsening the pulsation of the speed. Cogging torque is one of the causes of such torque ripple. Cogging torque is generated due to non-uniformity of magnetic energy in the gap between the stator and the rotor. Reducing this cogging torque improves the driving characteristics of the brushless motor.

In the permanent magnet embedded brushless motor illustrated in FIG. 1, the permanent magnet 11 is not an arc shape that is adapted to the shape of the outer circumferential surface of the rotor 10, but is a straight line, and thus the rotor 10 rotates as a permanent magnet ( 11) and the distance between the drive coil wound on the teeth 21 of the stator 20 is changed. Therefore, the arc-shaped permanent magnet is more cogging torque than the brushless motor disposed on the outer peripheral surface of the rotor (10).

FIG. 2 is a graph illustrating a change in the cogging torque according to the rotation angle of the rotor in the brushless motor of FIG. 1. It can be seen that the cogging torque pulsates within a range of about ± 0.12 Nm depending on the rotation angle of the rotor 10.

In order to reduce cogging torque, conventionally, the width of the magnetized permanent magnet is changed in the circumferential direction, or the width in the circumferential direction of the teeth 21 is increased, resulting in minimizing the width in the circumferential direction of the slot 23. And the like. However, this method is not only effective in reducing the cogging torque, but especially when the width of the slot 23 is narrowed, it becomes difficult to wind the driving coil on the teeth 21 of the stator 20. In addition, as a method widely used in recent years, there is also a method of giving a skew to the arrangement of the permanent magnet 11 of the rotor 10. In this method, a plurality of unit permanent magnets (11) in manufacturing the rotor 10, the unit permanent magnets are arranged so as to have a constant inclination angle along the axial direction of the rotor 10, the permanent magnet (11) There is a problem that the manufacturing process of the rotor 10 becomes very complicated due to the process of arrangement of the. On the contrary, although the teeth 21 of the stator 20 may have a constant skew along the axial direction, there is also a disadvantage in that the productivity is significantly reduced.

The present invention was developed to solve the above problems, to provide a brushless motor that can easily reduce the torque ripple due to cogging torque with a simple structure, and also to obtain a larger thrust ripple reduction effect. There is a purpose.

Other objects, specific advantages and novel features of the invention will become more apparent from the following detailed description and preferred embodiments in conjunction with the accompanying drawings.

An electric permanent magnet embedded brushless motor having a reduced cogging torque according to the present invention includes a cylindrical rotor, a plurality of permanent magnets embedded in the rotor and disposed at radial equal intervals, and the rotor. It includes a hollow cylindrical shape surrounding the stator, and a plurality of teeth protruding from the inner circumferential surface toward the center, and a plurality of driving coils wound around the plurality of teeth of the stator, the rotor is the outer surface and the plurality of permanent magnets Characterized in that the through channel is formed along the axial direction therebetween.

In the electric permanent magnet embedded brushless motor having a reduced cogging torque according to the present invention, it is preferable that the permanent magnet has a rectangular cross section perpendicular to the axial direction.

In addition, in the electric permanent magnet embedded brushless motor with reduced cogging torque according to the present invention, it is preferable that the through channel has a fan-shaped cross section perpendicular to the axial direction, and the fan-shaped arc faces the outer circumferential surface of the rotor. Do.

And in the electrostatic permanent magnet embedded brushless motor with reduced cogging torque according to the present invention, it is preferable that the through-channels are formed one at each end in the circumferential direction with respect to one permanent magnet.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the lifting module of the stud welding gun according to the present invention.

3 is a cross-sectional side view of one embodiment of a brushless motor according to the present invention.

The rotor 100 is a cylindrical member, and a rotating shaft is inserted into and fixed in the rotating shaft hole 110, or is integrally formed with the rotating shaft and installed to axially rotate with respect to an external conventional housing (not shown). The rotor 100 is provided with a plurality of permanent magnets 120, in particular, permanent magnet embedded brushless motor as shown in Figure 3 permanent magnets 120 as shown in Figure 3 from the outermost of the rotor to the central axis It is installed after entering a certain distance toward. That is, the permanent magnet 120 is not embedded in the outer circumferential surface of the rotor 100, but the permanent magnet 120 is embedded inside the rotor 100. In addition, the permanent magnet 120 has a rectangular cross section, and when compared to the permanent magnet having an arc-shaped cross-sectional shape in accordance with the outer peripheral surface shape of the rotor 100, it can be referred to as a straight permanent magnet. Such permanent magnets 120 are arranged in a plurality of radial equal intervals with respect to the rotor (100).

The stator 200 is a hollow cylindrical member and is disposed in a form surrounding the outer side of the rotor 100. The stator 200 may be protected by an external housing (not shown) and is fixed to the housing. Stator 200 is composed of a tooth (210) and the yoke portion 220, a plurality of teeth 210 is provided in a form protruding toward the center from the inner circumferential surface of the stator 200, yoke portion 220 ) Connects the teeth 210 in a ring shape. The driving coil is wound around each tooth 210 to generate magnetic flux when an external power source is applied.

On the other hand, the through-channel 130 is formed between the outer peripheral surface and the permanent magnet 120 embedded in the rotor 100. The through channel 130 is a hole formed through the axial direction of the rotor 100. Although the shape of the through channel 130 may be variably designed as needed, when the cross-sectional shape perpendicular to the axial direction is rectangular as shown in FIG. 4A, the through channel 130 is formed as shown by the dotted circle A. Concentration of magnetic flux at the edges of the saturation can cause saturation losses, and additional losses can occur as the magnetic path becomes longer. Therefore, as shown in Figure 4b, the cross section perpendicular to the axial direction of the through-channel 130 forms a fan shape, it is preferable that the fan-shaped arc is disposed so as to face the outer peripheral surface of the rotor (100). Then it is possible to minimize the concentration of the magnetic flux from the permanent magnet 120, it can also minimize the magnetic path. A plurality of through channels 130 may be provided as needed, but a pair of through channels 130 is preferably provided for one permanent magnet 120. In particular, when the permanent magnets 120 are straight, that is, when the cross section perpendicular to the axial direction of the permanent magnets 120 is rectangular, it is preferable that one through channel 130 is disposed at each of both longitudinal ends of the rectangular cross section. Do.

5 is a graph showing a change in cogging torque of the embodiment of FIG. In the brushless motor according to the present invention, it can be seen that the maximum value of the cogging torque stays at 0.07 Nm. This is a value reduced by more than 40% compared to 0.12 Nm, the cogging torque value of the brushless motor of FIG. Such a cogging torque reduction effect is obtained because the through channel 130 serves to disperse the magnetic flux from the permanent magnet 120 like a slot formed between the neighboring teeth 210 of the stator 200. This is especially noticeable when a pair of through channels 130 are arranged to correspond to both end portions of the permanent magnets 120 in the circumferential direction, respectively. That is, the permanent magnet 120 forms the through-channel 130 in the region closest to the teeth 210, the strongest magnetic flux is formed between the permanent magnet 120 and the teeth 210 to which the driving coil is wound. By distributing the flow of magnetic flux at the instant possible, the gap between the moment when the weakest magnetic flux is formed between the permanent magnet 120 and the tooth 210 is reduced.

An embodiment of the present invention described above and illustrated in the drawings should not be construed as limiting the technical idea of the present invention. The protection scope of the present invention is limited only by the matters described in the claims, and those skilled in the art can change and change the technical idea of the present invention in various forms. Therefore, such improvements and modifications will fall within the protection scope of the present invention, as will be apparent to those skilled in the art.

As described above, in the brushless motor according to the present invention, the through-channel disperses the magnetic flux, thereby reducing the unevenness of the magnetic force, and can easily reduce the torque ripple due to the cogging torque with a simple structure, and as a result, the thrust ripple reduction effect Can be obtained.

Claims (4)

With a cylindrical rotor, A plurality of permanent magnets embedded in the rotor and disposed at radial equal intervals; A stator having a hollow cylindrical shape surrounding the rotor, the plurality of teeth protruding from the inner circumferential surface toward the center thereof; A plurality of driving coils wound around a plurality of teeth of the stator, The rotor is a brushless motor having a through channel formed along the axial direction between the outer surface and the plurality of permanent magnets. The method of claim 1, The permanent magnet is a brushless motor, characterized in that the cross section perpendicular to the axial direction. The method according to claim 1 or 2, The through channel has a fan-shaped cross section perpendicular to the axial direction, the fan-shaped arc characterized in that toward the outer peripheral surface of the rotor. The method according to claim 1 or 2, The through channel is a brushless motor, characterized in that formed in one end at both ends in the circumferential direction for one permanent magnet.

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