JPH09182326A - Dc motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the development of a cogging torque causing a torque ripple by shifting circumferentially by respective specific phases the providing positions of respective magnets from their regular ones relative to a reference magnet. SOLUTION: For example, selecting as a reference magnet an arbitrary magnet 51 of four magnetic 51-54, the positions of the other three magnets 52-54 are shifted circumferentially from their regular positions relative to the reference magnet 51, i.e., 90 deg., 180 deg., 270 deg.. For example, which the number P of the poles of slots 6b is 12, the position of the opposite magnet 53 to the reference magnet 51 is shifted from its regular position of 180 deg. to 180 deg.±(2π/12)×(1/2)=180 deg.±15 deg.. Also, the positions of the adjacent magnets 52, 54 to the reference magnet 51 are shifted respectively from their regular positions of ±90 deg. to ±90 deg.±(2π/12)×(1/4)=±90 deg.±7.5 deg.. Therefore, the phases of the cogging torques of the respective magnets 51-54 are shifted not to increase as a whole the synthesized cogging torque out of them.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC motor designed to reduce cogging torque which causes torque ripple.

[0002]

2. Description of the Related Art Conventionally, as this type of DC motor, one having a structure as shown in FIGS. 5 and 6 is known. This DC motor 1 is provided with a bottomed cylindrical case 2 whose opening is covered with a lid 3, and inside of which a rotor 4 is provided.
And the stator 5 are arranged.

In the rotor 4, generally, a plurality of protrusions 6a and slots 6b are alternately formed in the rotor core 6 in the circumferential direction, and windings 7 are shown in the slots 6b (only one place is shown, the others are omitted).
It is composed of a slot winding type rotor wound
It is attached to the shaft 8. The stator 5 is composed of four magnets 51 to 54 fixed to the inner peripheral surface of the case 2 in the rotation direction of the rotor 4 at regular intervals, and has a predetermined magnetic gap G between itself and the rotor 4. Is formed.

Both ends of the shaft 8 are bearings 9 and 10.
Is rotatably rotatably supported, and one end thereof projects outside the lid 3 to form an output end. Further, a commutator 11 is fixed to the shaft 8, and a pair of brushes 1 is provided on the outer peripheral surface of the commutator 11.
2 are in contact. The brush 12 is housed in a brush holder 13 attached to the inner surface of the lid 3 so as to be orthogonal to the shaft 8 so as to be movable back and forth.
It is pressed against the commutator 11 by 4.

In the DC motor 1 having such a structure, when the external cord 16 is energized to excite the exciting coil 7, the rotor 4 rotates integrally with the shaft 8 by the action of the magnetic field. At this time, the magnetic flux fluctuates between when the magnetic poles of the rotor 4 pass the magnetic poles of the stator 5 and when they pass between the magnetic poles, so that torque fluctuations and periodic fluctuations in speed occur. As a result, the drive torque of the motor fluctuates (torque ripple). Such torque fluctuation and periodic fluctuation of speed are called cogging torque.

For example, as shown in the figure, in the case of the DC motor 1 having the stator 5 composed of magnets 51 to 54 having 4 poles and the rotor 4 having the 12 pole slots 6b, the magnets 51 to 54 are , 0 °, 90 °, 180
It is located at a regular position of 270 °. In this case, the cogging torque is equal to the cogging torque of one magnet × n times as shown in FIG. However, n is the number of magnets.

Therefore, various DC motors have been proposed in the past, which are designed to reduce the cogging torque which causes the torque ripple. A typical example of this is that the center points of the outer radius and the inner radius of the magnetic field forming magnet are eccentric to make the thickness thinner on both end sides than the central part, and the magnetic gap with the rotor core is made unequal. It is known that the slots of the rotor core are inclined (skewed) with respect to the axis. In the method of forming the magnet in which the center points of the outer radius and the inner radius are eccentric, the thickness of the magnet is not constant in the circumferential direction, it is thickest in the central portion, and decreases at both ends. For this reason, the magnetic gap between the rotor core and the magnetic core is the smallest in the center of the magnet, the magnetic field strength is the strongest, and the magnetic field strength is the weakest at the ends in the rotation direction. The fluctuation of the magnetic flux is reduced to reduce the generation of cogging torque. On the other hand, the method of skewing the slot of is the skew angle θ of the slot.
As a result, the facing area between the rotor core and the magnet gradually increases, so that it is possible to reduce the fluctuation of the magnetic flux when the magnetic poles of the rotor pass through the magnetic poles of the stator and to reduce the cogging torque as described above. .

[0008]

However, in the conventional DC motor in which the center points of the outer radius and the inner radius of the magnetic field forming magnet are eccentric to make the thickness thinner on both end sides than the central portion, the magnet can be manufactured. There is a problem in that the output torque is reduced because the magnetic gap G becomes large in addition to being troublesome. On the other hand, the conventional DC motor having skewed slots has a problem that the work of laminating the core and the work of winding are troublesome.

The present invention has been made in order to solve the above-mentioned conventional problems, and its purpose is to:
An object of the present invention is to provide a DC motor capable of reducing the generation of cogging torque which causes a torque ripple by arranging the magnets so as to be displaced in the circumferential direction.

[0010]

In order to achieve the above object, a DC motor according to the present invention includes a stator composed of four magnetic field forming magnets which are circumferentially spaced from each other on the inner peripheral surface of a case. In a direct current motor having a rotor in which an exciting coil is wound around a slot of a rotor core, the number of slot poles of the rotor core is P, and any one of the four magnets is used as a reference magnet. Place the magnet facing the magnet 18 from the position of the reference magnet.
The phase difference is 0 ° ± (2π / P) × (1/2), and the magnet adjacent to the reference magnet is 90 ° ± (2π / P) × (1/4) from the position of the reference magnet.
It is characterized in that it is provided only with a phase shift.

In the present invention, when any one arbitrary magnet is used as a reference magnet, the other three magnets are at regular positions with respect to the reference magnet.
Deviated in the circumferential direction from the positions of °, 180 °, and 270 °. For example, the magnet facing the reference magnet is
If the number of poles P in the slot is 12, 180 ° ± (2π
The position is 180 ± 15 ° from / 12) × (1/2). In addition, two adjacent magnets are 90 ° ± (2π
/ 12) × (1/4) to 90 ± 7.5 °. Therefore, the cogging torques of the respective magnets are out of phase and will not increase as a whole even if they are combined.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail based on the embodiments shown in the drawings. 1 is a sectional view of a DC motor according to the present invention, FIG. 2 is a sectional view taken along line II-II of FIG. 1, and FIG.
[Fig. 3] is a diagram showing the arrangement of magnets. The same members as those described in the section of the prior art are designated by the same reference numerals, and the description thereof will be omitted as appropriate. In these figures, in the present invention, four field forming magnets 51 to 54 provided on the inner peripheral surface of the case 2 are formed in the same shape with a uniform plate thickness and are unequal in the circumferential direction of the case 2. It is fixed at intervals. Therefore, the magnets 51 to 54
Are 0 °, 90 °, 180 °, and 270 °, which are the normal magnet positions in the conventional device shown in FIGS. 5 and 6.
It is out of alignment. The positions of such magnets 51 to 54 are determined as follows.

First, among the four magnets 51 to 54,
A certain arbitrary magnet, for example, the magnet 51 is used as a reference, and the reference magnet 51 is fixed at a position of 0 °.
Next, the position of the magnet 53 facing the reference magnet 51 is set to 180 ° ± (2π / P) × (1/2), and the positions of the remaining two magnets 52 and 54 adjacent to the reference magnet 51 are set to 90 °. ° ± (2π / P) × (1 /
Position 4). However, P is the number of poles of the slot 6b of the stator core 6, and is an even number of P = 2, 4, 6, ....

When the number of poles P of the slot 6b is 12, the position of the magnet 53 facing the reference magnet 51 is 180 ° ± (2π / 12) × (1/2) The position is 180 ± 15 °. In other words, it is displaced from the regular position of 180 ° by 15 °. In this case, assuming that the clockwise direction is positive and the counterclockwise direction is negative in FIG. 3, the magnet 53 is provided with a 15 ° offset from the normal position to the plus side, but may be provided with a 15 ° offset to the minus side. Good.

On the other hand, the positions of the two magnets 52 and 54 arranged on both sides of the reference magnet 51 are 90 ° ±±.
From (2π / 12) × (1/4), the position is 90 ± 7.5 °. Also in this case, the two magnets 52, 54
Are offset by 7.5 ° from the regular positions of 90 ° and 270 ° to the plus side, but they are offset by the minus side, or one of them is offset by the plus side and the other is offset by the minus side. May be. The other structure is the same as that of the conventional DC motor shown in FIGS.

FIG. 4 is a diagram showing the cogging torque of the DC motor according to the present invention. As is apparent from this figure, in the present invention, the magnets 51 to 54 are arranged at unequal intervals by displacing the magnets 51 to 54 from their normal positions, so that the phase of the cogging torque by each magnet can be shifted. Therefore, even if the respective cogging torques are combined, the overall cogging torque can be reduced.

Further, in the present invention, it is not necessary to form the magnets to have an unequal thickness or to provide a skew angle in the slot 6b by merely shifting the positions of the magnets 51 to 54, so that the manufacture is easy. , Can be manufactured at low cost.

[0018]

As described above, according to the DC motor of the present invention, the number of slot poles of the rotor core is P, and any one of the four magnets is used as a reference magnet and faces the reference magnet. The magnet is provided with a phase shift of 180 ° ± (2π / P) × (1/2) from the position of the reference magnet, and the magnet adjacent to the reference magnet is 90 ° ± (2π / from the position of the reference magnet.
Since the phase is provided by shifting by P) × (1/4), the phase of the cogging torque by each magnet can be shifted. As a result, it is possible to reduce the cogging torque as a whole and prevent the fluctuation of the drive torque. Further, since it is not necessary to form the magnets with unequal thickness and to provide the skew angle in the slot of the rotor core, the manufacturing is easy.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a DC motor according to the present invention.

FIG. 2 is an enlarged sectional view taken along line II-II of FIG.

FIG. 3 is a diagram showing an arrangement of magnets.

FIG. 4 is a diagram showing cogging torque of a motor according to the present invention.

FIG. 5 is a sectional view of a conventional DC motor.

FIG. 6 is a sectional view taken along line VI-VI of FIG. 5;

FIG. 7 is a diagram showing a cogging torque of a conventional motor.

[Explanation of symbols]

2 ... Case, 3 ... Lid, 4 ... Rotor, 5 ... Stator, 6 ... Rotor core, 6a ... Projection, 6b ... Slot, 7 ... Winding, 8
... shaft, 9 ... bearing, 11 ... commutator, 12 ... brush, 51-54 ... magnet.

Claims (1)

[Claims] 1. A stator composed of four magnetic field forming magnets, which are circumferentially spaced from each other on an inner peripheral surface of a case,
In a DC motor having a rotor in which an exciting coil is wound around a slot of a rotor core, the number of slot poles of the rotor core is P, and any one of the four magnets is used as a reference magnet. 180 ° ± (2π /
P) × (1/2) is provided with a phase shift, and the magnet adjacent to the reference magnet is provided with a phase shift of 90 ° ± (2π / P) × (1/4) from the position of the reference magnet. DC motor characterized by.