JP2783546B2 - Brushless motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a brushless motor used for a capstan motor for a VTR or the like.

(Prior Art) Recently, brushless motors have been used as motors as drive sources of tables in precision equipment such as video equipment and audio equipment such as video tape recorders (VTRs) and digital audio tape recorders (DATs).
The motor in such equipment is required to have high rotational accuracy, and therefore a motor with little torque ripple is demanded.

An example of this type of motor is shown in FIGS. 20 to 22. This motor is of a three-phase full-wave drive system.
In the same figure, 1 _a1 , 1 _a2 , 1 _b1 , 1 _b2 , 1 _c1 , 1 _c2 are stator coils attached to the stator substrate 2, and 3 is a ring-shaped attached to the rotor yoke 5 of the rotor 4. These rotor magnets face each other through a gap, and in this case, form an axial gap shape. The rotor magnet 3 is magnetized to eight poles as can be seen from FIG.

The stators 1 _a1 , 1 _a2 , 1 _b1 , 1 _b2 , 1 _c1 , 1 _c2 are energized in a predetermined order at an electrical angle of 120 degrees, so that a magnetic attraction force between the stator and the rotor magnets 3 is obtained. A repulsive force is generated to rotate the rotor 4. in this case,
The general air gap magnetic flux distribution of the rotor magnet 3 is shown in FIG. 23. At this time, since the three-phase full-wave drive system is used,
Waveforms A, B, and C whose phases are shifted by 120 degrees in electrical angle are combined with waveforms A ', B', and C 'that are inverted from each other. A motor torque is generated by such a magnetic field and a current flowing through the stator coils _1a1 , _1a2 , _1b1 , _1b2 , _1c1 , and _1c2 .

(Problems to be Solved by the Invention) However, the stator coils 1 _a1 , 1 _a2 , 1 _b1 , 1 _b2 , 1
_In this type of motor in which a substantially constant current _{flows through c1} and _1c2 , a torque ripple as shown in FIG. 24 occurs in the air-gap magnetic flux distribution of sine waveform synthesis as shown in FIG. As a result, there is a problem that uneven rotation occurs where the rotation speed of the rotor fluctuates, and wow and flutter and jitter occur in equipment using this motor. The present invention has been made in view of the above circumstances, and its purpose is to
An object of the present invention is to provide a brushless motor that can reduce torque ripple.

[Constitution of the Invention] (Means for Solving the Problems) The invention according to claim 1 includes a stator coil, and a ring-shaped rotor magnet opposed to the stator coil via an air gap, and is a three-phase full-wave drive system. In each of the magnetic poles of the rotor magnet, a substantially thick magnetic plate for flattening the vicinity of the center of the magnetic flux density is provided individually at substantially the center of the surface on the air gap side. It has features when it is attached.

The invention according to claim 2 includes a stator coil and a ring-shaped rotor magnet opposed to the stator coil via an air gap, and is driven by a three-phase full-wave drive system. In each magnetic pole, the ratio occupied by the ring-shaped unit magnet having a large magnetic strength at the center of the pole is made smaller than the ratio occupied near the pole boundary, and the magnetic flux density is reduced. Is characterized in that it is configured to flatten the vicinity of the center of the.

The invention according to claim 3 includes a stator coil, and a ring-shaped rotor magnet opposed to the stator coil via an air gap, and is driven by a three-phase full-wave drive system. The surface of the air gap side at the center of is formed in a substantially V-shaped concave shape having a deep central portion so as to flatten the vicinity of the center of the magnetic flux density, the depth of the concave portion is set to H [mm], and the width is set to W. The feature is that H / W is set to be 0.125 or more when [mm] is set.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the ratio of the magnetic plate to the surface of the gap side of each magnetic pole is equivalent to a conduction angle at a substantially central portion in an electrical angle of 180 degrees for one pole. The feature is that it is more than a corner.

According to the first aspect of the present invention, each of the magnetic poles of the rotor magnet has a uniform thickness that flattens the vicinity of the center of the magnetic flux density individually at substantially the center of the surface on the gap side. Since the magnetic plate is attached, the magnetic flux density is distributed so that the magnetic flux density in the air gap at the portion facing the magnetic plate is substantially constant. At this time, the torque ripple decreases as the current of each phase of the stator coil becomes constant and the ratio of the constant magnetic flux density increases.

According to the second aspect of the present invention, the rotor magnet is composed of a plurality of ring-shaped unit magnets having different magnetic intensities, and at each magnetic pole, a ring-shaped unit magnet having a large magnetic intensity at its pole center. Since the occupation ratio is made smaller than the occupation ratio in the vicinity of the pole boundary and the vicinity of the center of the magnetic flux density is flattened, the magnetic flux density distribution in each magnetic pole becomes substantially uniform. Therefore, the torque ripple can be reduced as described above.

According to the third aspect of the present invention, the surface of the center of each magnetic pole of the rotor magnet on the gap side is formed in a substantially V-shaped concave shape with a deep central portion so as to flatten the vicinity of the center of the magnetic flux density. When the depth of the concave portion is H [mm] and the width is W [mm], the H / W is set to be 0.125 or more, so that the magnetic flux density distribution at each magnetic pole becomes substantially uniform. . Therefore, the torque ripple can be reduced as described above.

According to the invention of claim 4, it is possible to greatly contribute to the flattening of the torque when the torque of each phase is combined, and the torque ripple is further reduced.

(Embodiment) Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 3 shows a longitudinal section of, for example, a capstan motor for a VTR. In FIG. 3, reference numeral 11 denotes a sleeve, and 12 denotes a stator substrate fixed to the sleeve 11. As shown in FIG. 4, stator coils 13 _a1 , 13 _a2 , 13
_{b1, 13 b2, 13 c1,} 13 c2 with is arranged, three position detecting elements 14, 14, 14 are disposed, distribution rotational speed detection frequency generator 15, further comprising a magnetoresistive element Has been established. Reference numeral 16 denotes a rotating shaft inserted and supported in the sleeve 11, and a lower end of the rotating shaft is provided with a rotor yoke 1 through a mounting portion 17a.
7 is fixed, and on the upper surface of the rotor yoke 17, the stator coils _13a1 , _13a2 , _13b1 , _13b2 , _13c1,.
A ring-shaped rotor magnet 18 is fixed so as to face 13 _c2 via a predetermined gap. A magnet 19 for a frequency generator is attached to a side edge of the rotor yoke 17.

The above stator coils _13a1 , _13a2 , _13b1 , _13b2 , _13c1 , 13
In the _c2, the stator coil 13 _a1 and the 13 _a2 are connected in series, also the stator coil 13 _b1 and 13 _b2 is connected 13 _c1 and 13 _c2 Togaotto s series. Each of these stator coils 1
3 _a1 , 13 _a2 , 13 _b1 , 13 _b2 , 13 _c1 , 13 _c2 have one of the three-phase full waves
A substantially constant current is supplied in accordance with a predetermined order determined by a drive method of 20-degree conduction, and magnetic attraction or repulsion is generated between the rotor magnet 18 and the rotor magnet 18, the rotor yoke 17. And the rotor 20 including the rotating shaft 16 rotates.

As shown in FIGS. 1 and 2, the rotor magnet 18 is magnetized to eight poles, and each magnetic pole is provided with a magnetic plate at a substantially central portion of the surface on the air gap side. 21 are respectively attached, for example, by bonding. This magnetic plate 21 is N
It is provided so as not to straddle the pole and S pole,
The magnetic plate 21 has a uniform thickness in order to flatten the vicinity of the center of the magnetic flux density.

As a result, as shown in FIG. 5, the magnetic flux density (indicated by the region L) in the gap facing the magnetic plate 21 becomes a substantially uniform distribution state.

Here, as is well known, the generated torque of this type of motor is expressed by the following equation (1).

T = k × (bA × IA + bB × IB + bC × IC) (1) k:
Constants related to the number of turns of the stator coil, etc. bA, bB, bC: A-phase, B-phase, C-phase currents In the case of 120-degree conduction, A-phase and B-phase, B-phase and C-phase,
In combination such as C phase and A phase, torque is always generated only in two phases.

As can be seen from the above equation, the torque ripple decreases as the ratio of the constant current of each phase and the constant magnetic flux density acting on the stator coil increases.
Therefore, according to this embodiment, as can be seen from FIG.
Since the region where the magnetic flux density is constant is wide, torque ripple can be reduced.

When the relationship between the ratio of the magnetic plate 21 to the width of the magnetic pole 21 and the torque ripple was examined by experiments, the results shown in FIG. 6 were obtained. That is, as the occupation ratio of the magnetic plate 21 to the magnetic poles increases, the torque ripple decreases accordingly. In particular, the magnitude of the magnetic plate 21 is shown in electrical angle the ratio among the one pole of the rotor magnet 18, stator coil 13 _a1, ... conduction angle or more to, for example, the rotor magnet in the case of a 120 ° conduction 18 1 pole 180 degrees almost 0.67
(Electrification angle of 120.6 degrees) or more, the torque ripple is further reduced as shown in FIG.

In particular, a magnetic plate 21 is separately provided for each magnetic pole, and the N pole and the S
Since it does not straddle the poles, a decrease in effective magnetic flux can be prevented, and a decrease in torque can be prevented. That is, if the magnetic plate is provided continuously at each magnetic pole, the magnetic plate straddles the N pole and the S pole. In this case, the magnetic flux is short-circuited through the magnetic plate, so Although the magnetic flux decreases and the torque decreases, this is not the case in the present embodiment.

Although the axial gap type motor is exemplified in the first embodiment, it may be a radial gap type motor. In this case, the motor shown in FIG. 7 shown as a second embodiment of the present invention will be described. As described above, the magnetic plate 23 may be individually attached to the inner peripheral surface side of the cylindrical ring-shaped rotor magnet 22 at substantially the center of each magnetic pole. In this case, the same effect as described above is obtained.

Next, Figs. 8 to 13 show a third embodiment of the present invention. The third embodiment differs from the first embodiment in the following points. As shown in FIGS. 8 to 10, the rotor magnet 24 is configured by integrating a first ring-shaped unit magnet 25 and a second ring-shaped unit magnet 26, The unit magnet 25 and the second ring unit magnet 26 are magnetized so as to have different magnetic intensities. The magnetic plate 21 is not used.

The first ring-shaped unit magnet 25 forms a part on the inner peripheral side with respect to the second ring-shaped unit magnet 26,
Further, the magnetic strength is set stronger than that of the second ring-shaped unit magnet 26. In this rotor magnet 24, when one pole is viewed, each unit has a shape in which the proportion of the first ring-shaped unit magnet 25 having strong magnetism at the pole center is smaller than the proportion shown near the pole boundary. The shape of the magnets 25 and 26 is set so that the vicinity of the center of the magnetic flux density is flattened. As a result, as shown in FIGS. 12 (a) to 12 (c) and FIG. 11, the magnetic flux density (region L) in the air gap facing each magnetic pole is obtained.
(Indicated by an electrical angle of 120 degrees)), the distribution becomes almost uniform. When the size of the torque ripple was examined, it was confirmed that the torque ripple was reduced as shown in FIG. FIG. 14 shows a fourth embodiment of the present invention. The fourth embodiment differs from the third embodiment in the following points. In the fourth embodiment, a cylindrical ring-shaped rotor magnet 27 in a radial gap type motor is shown, and also in this case, the magnet 27 is a first ring-shaped unit magnet 28 having a different magnetic strength. And a second ring-shaped unit magnet 29. This embodiment also has the same effect as the third embodiment.

FIGS. 15 to 18 show a fifth embodiment of the present invention. The fifth embodiment differs from the first embodiment in the following points. That is, the rotor magnet 30 is formed such that the surface on the gap side in each magnetic pole is formed in a V-shaped concave shape as the center portion is deeper. According to this, as shown in FIG. 17, one magnetic pole of the rotor magnet 30 is concave toward the center, so that the magnetic flux density in the air gap is uniform. As a result, torque ripple is reduced. In particular, when the ratio (H / W) of the depth H [mm] to the width W [mm] (which is the same as the magnetic pole pitch) of the concave portion 30a is 0.125 or more, as can be seen from FIG. Ripple is further reduced.

FIG. 19 shows a sixth embodiment of the present invention. The sixth embodiment differs from the fifth embodiment in the following points. In the sixth embodiment, a cylindrical ring-shaped rotor magnet 31 in a radial gap type motor is used.
The rotor magnet 31 is also shown in this case.
In this embodiment, the surface on the air gap side of each magnetic pole is formed in a substantially V-shaped concave shape with a substantially central portion being deep. In this embodiment, the same effect as that of the fifth embodiment can be obtained.

The present invention is not limited to the above-described embodiments.For example, the driving method is not limited to the full-wave driving method, and may be a half-wave driving method. The present invention is not limited to this example, and can be variously modified and implemented without departing from the gist thereof.

[Effects of the Invention] As is clear from the above description, the present invention can obtain the following effects.

The brushless motor according to claim 1, further comprising a stator coil and a ring-shaped rotor magnet opposed to the stator coil via a gap, and driven by a three-phase full-wave drive method, wherein the rotor magnet In each of the magnetic poles, a magnetic plate having a uniform thickness for flattening the vicinity of the center of the magnetic flux density is individually attached to a substantially central portion of the surface on the gap side, thereby reducing the torque ripple of the motor. And a decrease in torque can be prevented. Another advantage is that a conventional rotor magnet can be used as it is.

According to the brushless motor of claim 2, the brushless motor includes a stator coil and a ring-shaped rotor magnet opposed to the stator coil via a gap, and is driven by a three-phase full-wave drive system. Is composed of a plurality of ring-shaped unit magnets having different magnetic strengths,
In addition, in each magnetic pole, the ratio of the ring-shaped unit magnet having a high magnetic strength at the pole center is made smaller than the ratio occupied near the pole boundary to flatten the vicinity of the center of the magnetic flux density. It is possible to reduce the torque ripple. Incidentally, as a means for obtaining the same effect as above, it is conceivable to magnetize the opposite magnetic pole in one magnetic pole, but this complicates the magnetizing method and increases the cost. In this regard, in the brushless motor according to the second aspect of the present invention, since it is sufficient to combine the magnetized magnets by the conventional magnetizing method, the cost does not increase.

According to the brushless motor of claim 3, the brushless motor includes a stator coil and a ring-shaped rotor magnet opposed to the stator coil via a gap, and is driven by a three-phase full-wave drive method. The surface on the gap side at the center of each of the magnetic poles is formed in a substantially V-shaped recess having a deep center so that the vicinity of the center of the magnetic flux density is flattened, and the depth of the recess is H [mm]. Since the H / W is set to be 0.125 or more when the width is W [mm], the torque ripple of the motor can be reduced.
In particular, there is an advantage that the configuration is simple.

According to the brushless motor of the fourth aspect, it is possible to greatly contribute to the flattening of the torque when the torque of each phase is combined, and the torque ripple is further reduced.

[Brief description of the drawings]

1 to 6 show a first embodiment of the present invention. FIG. 1 is a perspective view of a rotor magnet, FIG. 2 is a plan view of the same, FIG. FIG. 5 is a bottom view of the stator substrate, FIG. 5 is a diagram showing a distribution state of the magnetic flux density, and FIG. 6 is a diagram showing a relationship between the occupation ratio of the magnetic plate to the magnetic pole and the torque ripple. FIG. 7 is a partial perspective view of a rotor magnet showing a second embodiment of the present invention. 8 to 13 show a third embodiment of the present invention. FIG. 8 is a diagram corresponding to FIG. 2, FIG. 9 is a plan view of the first ring-shaped unit magnet, and FIG. Plan view of the ring-shaped unit magnet of FIG. 11, FIG. 11 is a diagram showing a magnetic flux density distribution state of three-phase synthesis, FIGS. 12 (a) to (c) are magnetic flux density distribution diagrams of each phase, and FIG. It is a figure showing an occurrence state.
FIG. 14 is a view corresponding to FIG. 7 showing a fourth embodiment of the present invention. 15 to 18 show a fifth embodiment of the present invention. FIG. 15 is a diagram corresponding to FIG. 1, FIG. 16 is a partially enlarged side view of the rotor magnet, and FIG. 17 is a diagram corresponding to FIG. FIG. 18 is a diagram showing the relationship between the ratio of the depth / width of the concave portion and the torque ripple. FIG. 19 is a view corresponding to FIG. 7 showing a sixth embodiment of the present invention. 20 to 24 show a conventional example, FIG. 20 is a diagram corresponding to FIG. 3, FIG. 21 is a diagram corresponding to FIG.
FIG. 22 is a diagram corresponding to FIG. 2, FIG. 23 is a diagram corresponding to FIG. 11, and FIG. 24 is a diagram corresponding to FIG. In the figure, _13a1 , _13a2 , _13b1 , _13b2 , _13c1 , _13c2 are stator coils, 18 is a rotor magnet, 21 is a magnetic plate, 22 is a rotor magnet, 23 is a magnetic plate, 24 is a rotor magnet, 25 and 26 are ring-shaped unit magnets, 27 is a rotor magnet, 28 and 29 are ring-shaped unit magnets, 30 is a rotor magnet, and 31 is a rotor magnet.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H02K 21/12-21/24 H02K 29/00-29/14 H02K 1/27

Claims (4)

(57) [Claims] 1. A motor having a stator coil and a ring-shaped rotor magnet opposed to the stator coil via an air gap, and driven by a three-phase full-wave drive system, wherein each of the rotor magnets has a magnetic pole. A brushless motor characterized in that a uniform thick magnetic plate for flattening the vicinity of the center of the magnetic flux density is individually attached substantially at the center of the surface on the gap side. 2. A motor driven by a three-phase full-wave drive system comprising a stator coil and a ring-shaped rotor magnet opposed to the stator coil via an air gap. Each of the magnetic poles is made of a plurality of ring-shaped unit magnets having different magnetic strengths, and the ratio occupied by the ring-shaped unit magnet having a large magnetic strength at the pole center is made smaller than the ratio occupied near the pole boundary, and the center of the magnetic flux density is reduced. A brushless motor characterized by having a structure that flattens the vicinity. 3. A rotor driven by a three-phase full-wave drive system, comprising a stator coil and a ring-shaped rotor magnet opposed to the stator coil via a gap, wherein a center of each magnetic pole of the rotor magnet is provided. In order to flatten the vicinity of the center of the magnetic flux density, the surface on the gap side of the portion is formed in a substantially V-shaped concave with a deep central portion, the depth of the concave portion is H [mm], and the width is W [mm]. ] Brushless motor characterized in that H / W is set to be 0.125 or more when 4. The magnetic plate according to claim 1, wherein the ratio of the magnetic plate to the surface on the gap side of each magnetic pole is equal to or larger than the electrical angle corresponding to the conduction angle in a substantially central portion of the electrical angle of 180 degrees for one pole. The brushless motor according to claim 1.