JPH1198790A - Brushless dc motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain high output without changing the current-carrying capacity of a drive amplifier due to making multiple poles and reducing the size and cost, thereby increasing workability in manufacturing. SOLUTION: In a brushless DC motor, wherein a rotor iron core 21 having permanent magnets 29 placed on its surface is rotatably located in the axial direction inside a cylindrical stator iron core 20, the number of poles for the permanent magnet 29 of the rotor iron core 21 is 14, and the number of slots formed in the stator iron core 20 is 21 which allows concentrated winding of three-phase armature windings U, V, W, U', V', W'.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless DC (direct current) motor applied to a power source of a movable part of an FA (factory automation) product such as an industrial robot or a machine tool.

[0002]

2. Description of the Related Art In order to manufacture such a brushless DC motor with small size, high output and low cost, it is necessary to increase the energy density _Edc , which is the volume ratio of the motor to the output, and to simplify the motor structure. It is necessary to reduce the number of slots for arranging the armature windings as much as possible and to adopt a winding method with high workability.

[0003] Looking at the energy density _Edc , FIG. 5 shows that the rotor outer diameter and the winding method are the same, and the magnetic flux density of the stator core, the current density of the armature winding, and other electromagnetic characteristics are almost the same. Energy density E when the number of poles of the permanent magnet provided on the stator core is changed,
_Shows the value of _dc . As can be seen from this figure, it is necessary to increase the number of poles of the motor in order to increase the energy density _Edc .

FIG. 6 shows a cross-sectional view of a 6-pole, 18-slot brushless DC motor which has such a demand. A rotor core 2 is rotatably arranged in the stator core 1. Of these, slots 3 having 18 slots are formed in the stator core 1, and these slots 3 are provided with three-phase armature windings U, V, W, U ', V', W '.

The three-phase armature winding U 'indicates that the direction of current flow is opposite to that of the three-phase armature winding U, and the three-phase armature windings V' and W 'are also shown. Similarly, the direction in which the current flows in the three-phase armature windings V and W is opposite, and the U-phase band winding 4, the V-phase band winding 5, the W-phase band winding 6, and the U'-phase Band winding 7, V'-phase band winding 8, W'-phase band winding 9
And

Further, a permanent magnet 10 having six poles is provided on the rotor core 2. The winding method of such a motor is an integral slot lap winding in which the number of slots q for each pole is 1.0 (= 18 slots / 3 phases / 6 poles), and under the condition that the outer diameter of the rotor is limited. This method has the highest energy density and can be applied to other poles.

Further, the number of slots q per pole and phase is 1.0> q
For the range of> 0.5, for example, Japanese Patent Publication No. 7-999
FIG. 7 shows a cross-sectional view of a brushless DC motor having eight poles and fifteen slots, which employs the winding method described in Japanese Patent Publication No. 23. This motor is an example of eight poles and fifteen slots that are generally used most.

[0008]

By the way, in order to reduce the size and increase the output of the motor from the relationship between the energy density _Edc and the number of poles shown in FIG. 5, it is necessary to increase the number of poles as described above. a constant rotational speed N [rpm], since electrical frequencies when multi-polar is proportional to number of poles P, (a value proportional to the supply voltage) driving amplifier can be supplied voltage to the motor V _in
[V] to the voltage drop due to the armature inductance L _a [H] occupied _{2πN / 60P / 2L a · I} [V] is increased, minute was lowered a certain main magnetic flux from the above pole Φ _g [Wb], Output torque τ [Nm] by increasing current I [A]
Is designed to maintain For this reason, the current capacity of the drive amplifier increases, and the system cost increases.
It should be noted that the voltage V _in capable of supplying the drive amplifier to the motor,

[0009]

(Equation 1) And the output torque τ satisfies the following relational expression: τ = K ₂ · Φ _g · I (2) Here, _Ra is an armature winding resistance [Ω], and K ₁ is a coefficient [V / Wb / rp regarding an induced voltage.
m] and K ₂ are torque-related coefficients [Nm / Wb / A].

At this time, the number of slots may be a fractional slot winding where the number of slots per pole is q> 1.0 or 1.0> q
If a lap winding of> 0.5 is adopted, a good induced voltage waveform can be obtained, and motor characteristics such as torque ripple can be improved.

However, there is a problem that productivity is reduced due to the effect of increasing the number of slots by increasing the number of poles and complicating the armature winding, resulting in an increase in the cost of the motor. When the number of slots per phase is q = 1.0, it is necessary to take additional measures such as skew of the stator core 1 or the permanent magnet 10 and thinning of the edge of the permanent magnet 10 in order to obtain a good induced voltage waveform. However, there is a problem that the cost is further increased.

When the number of slots per phase per phase q <0.5, a large distortion, that is, an armature reaction occurs in the main magnetic flux due to the effect of the magnetomotive force generated by the current flowing through the armature winding.
Since a large iron loss occurs in the portion of the rotor core 2, there are problems such as a reduction in efficiency and the necessity of providing a new cooling means.

SUMMARY OF THE INVENTION The present invention provides a brushless DC motor which achieves high output without changing the drive amplifier current capacity due to multipolarization, and which is reduced in size and cost to improve manufacturing workability. With the goal.

[0014]

According to the first aspect of the present invention, in a brushless DC motor in which a rotor core having a permanent magnet disposed on a surface thereof in a stator core is rotatably disposed, the number of poles of the permanent magnet is set to 14, and The number of slots which allows the concentrated winding arrangement of the three-phase armature winding formed on the stator core is 2
1 is a brushless DC motor.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional configuration diagram of a brushless DC motor. A rotor core 21 is rotatably arranged in the axial direction inside the cylindrical stator core 20.

The outer peripheral surface of the rotor core 21 includes
A permanent magnet 29 having 14 poles is arranged. In addition,
A gap having a transmittance of 1 (generally, air) is formed between the permanent magnets 29, that is, between the N pole and the S pole.

FIG. 2 is a graph showing the relationship between the number of poles and the current when the same torque is generated.
Considering the relationship between multi-pole to increase _dc and the increase in drive amplifier current capacity, the figure shows that
4 is adopted.

By employing the number of poles 14, a motor having the highest energy density _Edc can be realized without changing the drive amplifier capacity. On the other hand, the stator core 20 is formed with a slot 22 having the number of slots 21 (the number of slots per pole per phase q = 0.5).

By adopting the number of slots of 21, the concentrated winding which is excellent in the motor characteristics and the most excellent in mass production in terms of winding workability is employed. These slots 22 have three-phase armature windings U, V,
W, U ', V', W 'are given.

Here, the three-phase armature winding U 'indicates that the current flows in the opposite direction to the three-phase armature winding U, as described above. 3 for W '
This indicates that the direction of current flow is opposite to the phase armature windings V and W, and the U-phase winding 23, the V-phase winding 24, the W-phase winding 25, and the U'-phase winding 26, V 'phase band winding 27, W
′ -Phase band winding 28. Note that these windings U, V,
W and windings U ', V', W 'are windings U, V, W (forward)
And the windings U ′, V ′, W ′ (return) form a set of coils.

As described above, the permanent magnet 29 of the rotor core 21
And three-phase armature windings U, V, W, U ', V', and W 'formed on the stator core 20 have a number of slots 21 enabling concentrated winding arrangement. ,
By increasing the energy density E _dc by increasing the number of poles to 14 poles, it is possible to reduce the motor volume by 10 to 15% as compared with the related art. In addition, the amount of magnet used can be reduced by 30 to 40% with the same demagnetization proof strength as compared with the conventional product, and the cost can be reduced. Further, there is no change in the current capacity of the drive amplifier due to the increase in the number of poles, and a power semiconductor element equivalent to a conventional motor can be used.

Further, by setting the number of slots to 21 (the number of slots per pole per phase q = 0.5), the winding coefficient is slightly lower by 0.866, but it is a small slot with good motor characteristics. A centralized winding system in which winding work can be performed by an automatic machine can be adopted, thereby improving workability in manufacturing.

The reason why the number of slots is set to 21 is that the main magnetic flux density distribution of the gap pole magnetic flux distribution of the 8-pole and 9-slot motor shown in FIG. As shown in the figure, the main magnetic flux is distorted due to the effect of the magnetic flux generated by the armature winding current, and this becomes a rotating magnetic field inside the motor.
A change in magnetic flux occurs in the rotor portion, and the core 2
This is because an eddy current flows through the 0, 21 and permanent magnets 29 (resistivity has substantially the same characteristics as an iron core), iron loss occurs, and efficiency is reduced. Further, in order to cool the heat generated by the iron loss of the rotor portion, it is necessary to provide a new cooling means, which leads to an increase in manufacturing cost.

On the other hand, when the number of slots is 21, the main magnetic flux is distorted due to the effect of the magnetic flux generated by the armature winding current as shown in the gap main magnetic flux density distribution diagram of the 14-pole 21-slot motor in FIG. Never.

[0025]

As described above in detail, according to the first aspect of the present invention, in a brushless DC motor in which a rotor core having a permanent magnet disposed on a surface thereof in a stator core is rotatably disposed, the number of poles of the permanent magnet is 14, and the number of slots is 21 so that the three-phase armature windings formed on the stator core can be concentratedly arranged. Therefore, high output can be realized without changing the drive amplifier current capacity due to multi-poles, and the size can be reduced. ,
It is possible to provide a brushless DC motor that can be manufactured at low cost and can improve the workability of manufacturing.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram showing an embodiment of a brushless DC motor according to the present invention.

FIG. 2 is a diagram showing the relationship between the number of poles when the same torque is generated and the current.

FIG. 3 is a gap main magnetic flux density distribution diagram of an 8-pole, 9-slot motor.

FIG. 4 is a gap main magnetic flux density distribution diagram of a 14-pole 21-slot motor.

FIG. 5 is a diagram showing a value of an energy density E _dc when the number of poles of a permanent magnet is changed.

FIG. 6 is a cross-sectional configuration diagram of a conventional 6-pole 18-slot brushless DC motor.

FIG. 7 is a cross-sectional configuration diagram of a conventional 8-pole 15-slot brushless DC motor.

[Explanation of symbols]

 Reference numeral 20: stator core, 21: rotor core, 22: slot, 23: U-phase band winding, 25: W-phase band winding, 25: W-phase band winding, 26: U'-phase band winding, 27: V 'Phase band winding, 28 ... W' phase band winding, 29 ... permanent magnet.

Claims (1)

[Claims] 1. A brushless DC motor in which a rotor core in which a permanent magnet is disposed on the surface of a stator core is rotatably disposed, wherein the number of poles of the permanent magnet is set to 14, and the three-phase electric motor is formed in the stator core. A brushless DC, wherein the number of slots for allowing a concentrated winding arrangement of slave windings is 21.
motor.