JP2003047181A - Brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a brushless motor which effectively reduces cogging torque. SOLUTION: Each tooth 20 of a stator 22 of the brushless motor is formed on a collar 24, which extends the end parts of the rotor 16 side in the circumferential direction (the X direction in Drawing 2). The collar 24 has a gap with a facing permanent magnet 14, and in such a case, the gap is formed larger at both ends in the circumferential direction (at G1 in Drawing 2) comparing with the center side in the circumferential direction (at G2 in Drawing 2), and the surface of the collar 24 facing the permanent magnet 14 is formed flat.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless motor.

[0002]

2. Description of the Related Art Brushless motors are widely used as drive devices for office automation equipment and information equipment.

Accurate drive control performance and rotation control performance are required for brushless motors used in such equipment.

By the way, the brushless motor has a structure having a stator in which a plurality of teeth are formed at equal intervals in the circumferential direction, and the space between the teeth is opposed to the permanent magnet in the space between the teeth. The magnetic resistance of the magnetic pole (hereinafter, referred to as the rotor magnetic pole) is increased. Therefore, there is a difference in the rotational torque of the rotor between when the magnetic poles of the rotor face the space between the teeth and when the magnetic poles face the teeth. Such torque fluctuation that occurs during rotor rotation is called cogging, and the magnitude of torque fluctuation due to cogging is called cogging torque.

An example in which a large cogging torque is generated is shown in FIG.
Shown in. In FIG. 5, the horizontal axis represents the rotation angle (time) and the vertical axis represents the cogging torque value. In this case, the cogging torque of the motor having an average rotor rotation torque value of about 20 mN · m is about 5.4 mN · m when measured five times. Here, the difference between the maximum torque value and the minimum torque value for one round measurement was taken as the cogging torque for one measurement, and the average value for the five measurements was calculated.

When the cogging torque is large, the rotation speed of the motor fluctuates, the smoothness of rotation is impaired, and high performance cannot be achieved.

In order to reduce the cogging torque, for example, the number of magnetic poles of the permanent magnet and the number of teeth are set to a specific combination condition to increase the pulsation number of the cogging torque to increase the magnitude of the cogging torque per unit pulsation. Are being studied. By providing a ring made of a magnetic material in the gap between the permanent magnets and the teeth, the magnetic resistance changes when the rotor magnetic poles face the space between the teeth and when they face the teeth. Methods such as reducing the are also being studied.

[0008]

However, the above-mentioned conventional measures for reducing the cogging torque do not always give a sufficient effect.

The present invention has been made in view of the above problems, and an object thereof is to provide a brushless motor in which the cogging torque is effectively reduced.

[0010]

A brushless motor (10) according to the present invention has a permanent magnet (14) having S poles and N poles alternately magnetized at equal intervals on the outer circumference of a rotary shaft (12). A stator (22) in which a rotor (16) and a plurality of teeth (20) wound with a plurality of phase coils (18) surrounding the outer peripheral surface of the rotor (16) are formed at equal intervals in the circumferential direction. In the brushless motor (10), the end of the tooth (20) on the rotor (16) side is formed in a collar portion (tooth tip, salient pole 24) protruding in the circumferential direction. The magnetic resistance increasing mechanism (G1, A) for increasing the magnetic resistance of the magnetic poles of the opposing portion of the permanent magnet as compared with the center side in the circumferential direction of (24) is provided at both ends in the circumferential direction of the collar portion (24). It is characterized in that (the invention according to claim 1).

As a result of intensive studies by the present inventors, the Maxwell attraction force suddenly increases between the boundary portion between the S and N magnetic poles of the permanent magnet and the edge portion of the collar portion of the tooth, which increases the cogging torque. It was found to be one of the causes.

Therefore, according to the above configuration of the present invention,
The magnetic resistance of the magnetic poles on both ends (edge portions) in the circumferential direction of the collar is made larger than that on the center side in the circumferential direction of the collar, in other words,
The cogging torque can be reduced by weakening the Maxwell suction force on both end sides of the collar portion in the circumferential direction as compared with the center side of the collar portion in the circumferential direction.

In this case, the magnetic reluctance increasing mechanism has a gap (G) between the flange portion (24) and the permanent magnets (14) which are formed larger on both circumferential sides than on the central side in the circumferential direction.
1) (the invention according to claim 2), and the magnetic resistance increasing mechanism is formed in an arc shape, and the collar portion (24
the edge (A) of the portion facing the permanent magnets (14) on both ends in the circumferential direction of (a) (the invention according to claim 3);
It is preferable that the magnetic resistance increasing mechanism is the collar portion having a radius of curvature which is twice or more the radius of the rotor (the invention according to claim 4).

It should be noted that the reference numerals in the above parentheses are the reference numerals of the corresponding components in the embodiments to be described later in order to facilitate understanding, and the present invention is limited to the embodiments. Not something to do.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION A preferred embodiment of a brushless motor according to the present invention (hereinafter referred to as the present embodiment) will be described below with reference to the drawings.

A brushless motor according to this embodiment will be described with reference to FIGS.

In FIG. 1 showing a schematic cross section in a direction orthogonal to the rotation axis of the brushless motor according to the present embodiment,
The brushless motor 10 includes a rotor 16 having a permanent magnet 14 magnetized around the outer circumference of a rotating shaft 12 at alternate and equal intervals of S poles and at equal intervals, for example, a total of 16 divisions.
For example, a 3-phase coil (1 in FIG. 1) surrounding the outer peripheral surface of 6
A stator 22 having, for example, twelve teeth 20 wound around each of which only one portion is shown) 18 is wound, is provided.

The teeth 20 are formed on the flanges (tooth tips) 24 whose ends on the rotor 16 side project in the circumferential direction (X direction in FIG. 2). The collar portion 24 has a gap between the facing permanent magnets 14, and in this case, the gap is larger on both circumferential side ends (G1 in FIG. 2) than on the circumferential center side (G2 in FIG. 2). The flange portion 24, which is formed and faces the permanent magnet 14, has a flat surface (a straight line in the cross-sectional view). On the other hand, the conventional collar portion 2 shown by the broken line in FIG.
It is formed in a curved surface shape (arc shape in a sectional view) having a radius of curvature substantially the same as the radius of the rotor 16, and has a uniform gap (g in FIG. 2) over the entire surface of the collar portion 24.
Therefore, in other words, the collar portion 24 of the present embodiment has an infinite radius of curvature in comparison with the conventional collar portion 2. The large gap of the collar portion 24 constitutes a magnetic resistance increasing mechanism.

The result of measuring the cogging torque of the brushless motor 10 is shown in FIG. The brushless motor 10 is
It can be seen that the cogging torque value is smaller than that in the conventional example of FIG. Specifically, the cogging torque of the motor having an average rotor rotation torque value of about 20 mN · m is 4.48 for the first time, 4.96 for the second time, 4.43 for the third time, and 4.43 for the fourth time. The average of 4.39 for the fifth and 4.40 for the fifth time is 4.51 (the unit is mN · m for each). The cogging torque value is reduced by about 20% compared to the conventional example.

In the brushless motor according to the present embodiment, in the conventional case, a sudden change that increases the magnetic resistance value of the magnetic poles is generated, which increases the Maxwell attraction force and increases the cogging torque. Since the gaps on both sides (edges) in the circumferential direction of the part are formed larger than in the center side in the circumferential direction of the collar, the magnetic resistance value of the magnetic pole becomes small and sudden fluctuations are eliminated, so the Maxwell suction force is small. Therefore, the cogging torque is small.

It is sufficient for the collar portion to be formed in a curved shape having a radius of curvature that is at least twice the radius of the rotor, and it may be formed in a reverse curved shape in which both circumferential ends warp outward.

Next, a modified example of the collar portion (magnetic resistance increasing mechanism) of the tooth will be described with reference to FIG.

Collar 24a of teeth 20a according to a modification
Is chamfered at the edge (indicated by arrow A in FIG. 4) of the portion facing the permanent magnets 14 at both ends in the circumferential direction, which are usually formed at a substantially right angle as shown for the collar portion 2 in FIG. Are formed in an arc shape. The form of the collar portion 24a constitutes a magnetic resistance increasing mechanism. As with the conventional example, the entire flange portion 24a has a curved surface facing the permanent magnet 14.

Collar 24a of teeth 20a according to a modification
Since the edge is formed into an arc shape by forming the corners of the edge, the phenomenon of concentration of the magnetic flux, which has conventionally occurred at the edge portion, is alleviated. As a result, similar to the brushless motor according to the present embodiment, the cogging torque is reduced. Can be reduced.

Note that, regardless of the above-described present embodiment, the flange portion 24 of the present embodiment and the flange portion 24a of the modified example are used as the shape of the edge of the portion facing the permanent magnets 14 on both ends in the circumferential direction. You may combine each form of these suitably.

[0026]

According to the brushless motor of the first aspect of the present invention, the magnetic resistance increasing mechanism for increasing the magnetic resistance of the magnetic poles of the opposing portion of the permanent magnet as compared with the circumferential center side of the collar portion of the tooth is provided with a magnetic resistance increasing mechanism. Since it is provided at both ends in the direction, cogging torque can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a brushless motor according to an embodiment of the present invention in a direction orthogonal to a rotation axis.

FIG. 2 is a diagram showing teeth of the brushless motor of FIG.

FIG. 3 is a graph showing a cogging characteristic of the brushless motor shown in FIG.

FIG. 4 is a diagram showing teeth of a brushless motor according to a modified example of the present embodiment.

FIG. 5 is a graph showing a cogging characteristic of a conventional brushless motor.

[Explanation of symbols]

10 brushless motor 12 rotation axes 14 permanent magnet 16 rotor 18 coils 20, 20a Teeth 22 Stator 24, 24a Collar part

Claims (4)

[Claims] 1. A rotor having a permanent magnet in which S poles and N poles are magnetized alternately and equidistantly on the outer circumference of a rotating shaft, and a plurality of coils each having a plurality of phase coils surrounding the outer peripheral surface of the rotor are wound. A brushless motor having a plurality of teeth formed at equal intervals in the circumferential direction, the rotor-side ends of the teeth being formed in a flange portion projecting in the circumferential direction, in the circumferential direction of the collar portion. A brushless motor, characterized in that magnetic resistance increasing mechanisms for increasing the magnetic resistance of the magnetic poles of the opposing portion of the permanent magnet are provided at both ends in the circumferential direction of the flange portion as compared with the central side. 2. The magnetic resistance increasing mechanism is a gap formed between the permanent magnets formed on both ends in the circumferential direction of the flange portion so as to be larger than those on the center side in the circumferential direction.
Brushless motor described. 3. The brushless motor according to claim 1, wherein the magnetic resistance increasing mechanism is an edge of a portion which is formed in an arc shape and which faces the permanent magnets on both ends in the circumferential direction of the flange portion. . 4. The brushless motor according to claim 1, wherein the magnetic resistance increasing mechanism is the collar portion having a radius of curvature that is twice or more the radius of the rotor.