Motor having permanent magnets received therein

A motor having permanent magnets received therein includes a rotor having a plurality of circular sheet irons deposited in turn, a plurality pairs of magnet receiving slots formed through the deposited sheet irons at a predetermined angle toward the outer surface of the rotor, and permanent magnets of different polarities received into the magnet receiving slots, wherein a magnetic flux leakage preventive groove having a predetermined width and depth is formed at the outer surface of the rotor at the center between the pair of magnet receiving slots.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a brushless motor having permanent magnets 
received therein, and more particularly, to a motor having permanent 
magnets in which the magnets are disposed so as to have uniform magnetic 
flux and a rotor for decreasing magnetic flux leakage and enhancing the 
usefulness of the magnetic flux is adopted. 
2. Description of the Related Art 
Brushless motors are gaining in popularity as the home appliances or 
industrial equipment becomes to have high performance, lighter weight, and 
more compact. In addition, motor control technique is being widely used 
due to the development in the areas of semiconductor technique or 
substances, which enhances the reliability of brushless motors. 
FIG. 1 shows the structure of brushless motors, FIG. 2 shows the waveform 
of the current flowing at each phase shown in FIG. 1, FIG. 3A is a vector 
diagram illustrating the magnetic field generated from the current, and 
FIGS. 3B to 3E are vector diagrams illustrating the magnetic field 
generated according to each angle at which a rotor rotates. 
As shown in FIG. 1, around a rotor 1 having two poles N and S, stator coils 
Lu, Lv, and Lw at which three phase current flows are arranged at 
120.degree.. In addition, one end portions of the stator coils Lu, Lv, and 
Lw are connected to a voltage supply source Vcc, respectively, and the 
other end portions of the stator coils Lu, Lv, and Lw are connected to 
switching elements Qu, Qv, and Qw, respectively. Switching elements are 
turned on or off according to the control of a driving controller 2, 
thereby conducting current to the coils. 
As an example of using 180.degree. conducting method, if it is assumed that 
the current flows each phase as shown in FIG. 2, the magnetic field is 
emitted at a direction from the winded coils toward rotor 1. Since the 
coils are disposed at 120.degree., respectively, the magnetic field 
emitted therefrom is also at 120.degree., as shown in FIG. 3A. 
As shown in FIG. 3B, current flows at coils Lu and Lv when an electrical 
angle is 0.degree.. That is, when the control signal from driving 
controller 2 turns the switching elements Qu and Qv on, the current flows 
at coils Lu and Lv, and magnetic fields Mu and Mv are generated. Then, a 
combined magnetic field MT1 is formed, and rotor 1 rotates in clockwise 
direction as shown in FIG. 3B, being affected by the combined magnetic 
field MT1. 
When the electrical angle exceeds 60.degree. as shown in FIG. 2, the 
current at coil Lv is cut off, and generating the magnetic field Mv which 
makes rotor 1 to be rotated in counterclockwise direction is restricted. 
In other words, the current flows only at the coil Lu, which generates 
only the magnetic field Mu. Here, rotor 1 rotates as shown in FIG. 3C, and 
magnetic filed Mu vector faces the center of N-pole, thereby rotating 
rotor 1 at the same direction. 
When the electrical angle exceeds 120.degree. as shown in FIG. 3D, the 
current is provided for coils Lu and Lw, and magnetic fields Mu and Mv are 
generated. Then, a combined magnetic field MT2 is formed, and rotor 1 
rotates, being affected by the combined magnetic field MT2. When the 
electrical angle exceeds 180.degree. as shown in FIG. 3E, rotor 1 rotates 
in counterclockwise direction. At such a state, the current for generating 
magnetic fields Mu and Mv that make rotor 1 to be rotated in 
counterclockwise direction is cut off, and the current is provided only 
for coil Lu so as to generate magnetic field Mw for rotating in clockwise 
direction. 
As shown in FIGS. 3A to 3F, the magnetic field generated at the stator 
coils appropriately controls the current of each phase, to thereby form a 
rotating magnetic field. The rotor rotates according to the rotating 
magnetic field. 
The rotating magnetic field of brushless motors is made up of the combined 
magnetic field of each phase. Therefore, the size of the rotating magnetic 
field is not regular every moment, and the torque generated by the 
rotating magnetic field is not uniform, which causes a ripple. In 
addition, the combined magnetic field interacts with the permanent magnets 
of the rotor according to the structure of the rotor. However, if the 
combined magnetic field that passes through the interior of the rotor 
aggregates densely at a specific portion, the magnetic reluctance 
increases. If the rotor has an inappropriate structure, the magnetic flux 
generated from the permanent magnet leaks to the adjacent magnets, which 
degrades a motor efficiency. 
FIG. 4A shows an example of the iron sheet used for a conventional 
brushless motor, and FIG. 4B is a section view showing a motor to which 
the rotator having a series of iron sheet is applied. 
To reduce the core loss generated from rotor 1, a core 40 where a series of 
iron plates made up of a silicon are deposited is used for rotor 1. 
Accordingly, rotor 1 in section view is shaped same as the core. Core 40 
has at a center thereof a hole 41 into which a rotating shaft is to be 
pressed and fixed, holes 42 into which bolts are inserted so as to fix 
core 40, and slots 44 into which permanent magnets are to be received 
oppositely to each other from the rotating shaft. The magnetic flux 
generated from the permanent magnets received in slots 44 passes through 
the gap between rotor 1 and a stator 45 and flows toward a teeth 46 of 
stator 45. In other words, as shown in FIGS. 4B and 5, the magnetic flux 
generated from stator 45 travels teeth 46, core 40, and the permanent 
magnets received in slots 44, and travels again core 40, permanent 
magnets, and teeth 46, to thereby form a closed loop. 
However, since the outer surface of the core is shaped as a circle 
centering from the shaft of the rotor, the portion A of the magnetic flux 
from the permanent magnets directly flows toward the opposite magnetic 
poles of the permanent magnets, as shown in FIG. 5. That is, all of the 
magnetic flux from the end of the permanent magnets received in the slots 
does not flow toward to the stator, which means the magnetic flux 
partially leaks as shown in portion A of FIG. 5. This occurs because the 
core at the end of the permanent magnet is shaped as a circle, which 
provides a sufficient core area for the flowing of the magnetic flux. 
The leakage magnetic flux is useless since it does not affect to the 
rotation of the rotor, which degrades a motor efficiency. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a brushless 
motor having permanent magnets in which the structure of the core the 
rotor is modified so as to minimize the leakage magnetic flux, to thereby 
enhance motor efficiency and reduce the cost of the substances of the 
core. 
It is another object of the present invention to provide a brushless motor 
having permanent magnets in which the core of the rotor has recess 
portions at the outer surface thereof to which the permanent magnet having 
different polarities is adjacent, so as to minimize the leakage magnetic 
flux, to thereby reduce a torque ripple and minimize the noise and 
vibration. 
To achieve the above objects and other advantages, there is provided a 
motor having permanent magnets received therein including a rotor having a 
plurality of circular sheet irons deposited in turn, a plurality pairs of 
magnet receiving slots formed through the deposited sheet iron at a 
predetermined angle toward the outer surface of the rotor, and permanent 
magnets of different polarities received into the magnet receiving slots, 
wherein a magnetic flux leakage preventive groove having a predetermined 
width and depth is formed at the outer surface of the rotor at the center 
between the pair of magnet receiving slots. 
Preferably, the distance between the outer end of the magnet receiving slot 
and the outer surface of the rotor is 0.5 mm or shorter, and the distance 
between the sidewall of the magnetic flux leakage preventive groove and 
the sidewall of the magnet receiving slot adjacent to the magnetic flux 
preventive groove is 0.5 mm or shorter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention now will be described more fully hereinafter with 
reference to the accompanying drawings, in which preferred embodiments of 
the invention are shown. This invention may, however, be embodied in many 
different forms and should not be construed as limited to the embodiments 
set forth herein; rather, these embodiments are provided so that this 
disclosure will be thorough and complete, and will fully convey the scope 
of the invention to those having skill in the art. 
Referring to FIGS. 6A, a sheet iron 50 of a 4 pole rotor 100 has at the 
center thereof a hole 41 into which a rotating shaft (not shown) is to be 
fixed, permanent magnets with a predetermined length and which are 
disposed oppositely and in parallel with the radius direction from the 
center of rotor 100, and first permanent magnet receiving slots 51 to 54 
and second permanent receiving slots 61 to 68 which are formed in such a 
manner that four pairs of permanent magnets are disposed in ladder-shape 
toward the outer surface of sheet iron 50. Planar-type permanent magnets 
are fixed into magnet receiving slots 51 to 54 and 61 to 68. Preferably, 
the angle between two opposing permanent magnets disposed in ladder-shape 
is 120.degree. to 170.degree., and more preferably, 150.degree., 
considering the smooth flow of the magnetic flux through the rotor. 
Preferably, thickness of the permanent magnet is 2% to 8% of the 
circumference of the rotor, and the permanent magnets are disposed in such 
a manner that the magnetic poles of same polarity are opposed to each 
other by 180.degree. centering from the rotating shaft. 
For example, second permanent magnet receiving slots 67 and 68 are disposed 
to be more adjacent as they go away from the center toward the outer 
surface of the rotor. 
A magnetic flux leakage preventive groove 110 shaped as a recess is formed 
at the outer surface of the rotor. Magnetic flux leakage preventive groove 
110 is formed in such a manner that the center thereof is positioned at a 
point where the centerline between permanent magnetic receiving slots 67 
and 68 crosses the circumference of the rotor. 
Referring to FIG. 6B, magnetic flux leakage preventive groove 110 includes 
portion (a) between the end of permanent magnet receiving slot 68 and the 
outer surface of the rotor, portion (b) between the sidewall of permanent 
magnet receiving slot 63 and the sidewall of magnetic flux leakage 
preventive groove 110, and portion (c) which is the bottom surface of 
magnetic flux leakage preventive groove 110. Here, preferably, length L1 
of portion (a), length L2 of portion (b), and length L3 which is the depth 
of magnetic flux leakage preventive groove 110 excluding length L1 are 0.5 
mm or shorter, respectively. If they are longer than 0.5 mm, the magnetic 
flux leakage prevention effect will be decreased. 
Length L3 is longer than the air gap between the stator and the rotor, 
which prevents the useless magnetic flux caused by the circular outer 
surface of the rotor, i.e., the magnetic flux leakage. 
In some cases, length L3 is within a range that does not exceed the 
thickness of the permanent magnets, and the width of magnetic flux leakage 
preventive groove does not exceed 1.2 times of the thickness of the 
permanent magnets. In such a manner, the magnetic flux generated at the 
end of the magnet may not pass magnetic flux leakage preventive groove 
110, and pass teeth 46 of stator 45. 
An operation of the motor of the present invention operates as follows. 
Referring to FIGS. 7A and 7B, the magnetic flux passes through the air gap 
between the rotor and the stator, teeth 46, and the main body of rotor 
100, and enters the adjacent permanent magnet of opposite polarity. The 
magnetic flux intends to flow via the medium having excellent magnetic 
permeability, and has less magnetic reluctance as the magnetic flux path 
is shorter. Therefore, it is preferable to make the magnetic circuit as 
short as possible. In addition, if the magnetic flux is distributed 
densely at a certain position, the magnetic reluctance increases. 
Therefore, it is preferable to uniformly distribute the magnetic flux. 
As shown in FIGS. 7A and 7B, the magnetic flux is distributed uniformly, 
and specifically, in the rotor, the magnetic flux line in the magnet 
proceeds in one direction. 
The magnetic flux leakage where the magnetic flux generated from the end of 
the permanent magnet directly passes the permanent magnets can be reduced 
by magnetic flux leakage preventive groove 110 which is designed to have a 
magnetic reluctance smaller than those between the permanent magnet and 
teeth 46 and those between the end of the permanent magnet and the end of 
the adjacent permanent magnet. Thereby, the magnetic flux leakage is 
reduced, and the magnetic flux generated from the end of the permanent 
magnet passes through teeth 46, which substantially enhances a motor 
efficiency. 
According to the present invention, the amount of torque generated from the 
magnetomotive force of the stator is further increased than the 
conventional art assuming that the number of turns of coils and the 
current consumption are the same. In addition, the torque ripple is 
enhanced, too. 
In the present invention, arrangement of magnets of the rotor is enhanced, 
and the magnetic flux leakage preventive groove having an appropriate size 
is formed at the outer surface of the rotor, to thereby reduce the 
magnetic flux leakage and the core loss in the rotor. Thus, an overheating 
during the operation of the motor is prevented, and the useful magnetic 
flux is increased. Ultimately, further large amount of torque can be 
achieved, and the motor can be operated in a high efficiency. The same 
amount of torque can be obtained with the reduced size of the motor. In 
addition, the magnetic reluctance can be reduced by making the path along 
which the magnetic flux flows to be short as possible. As a result, 
maximum amount of torque can be obtained with the same current of the 
stator. 
In summary, grooves shaped as a recess are formed at the outer surface of 
the rotor to which the permanent magnets of different polarities are 
adjacently positioned, which minimize the magnetic flux leakage. A high 
torque can be obtained with the same power consumption, the torque ripple 
can be reduced, and the noise and the vibration can be minimized. 
This invention has been described above with reference to the 
aforementioned embodiments. It is evident, however, that many alternative 
modifications and variations will be apparent to those having skill in the 
art in light of the foregoing description. Accordingly, the present 
invention embraces all such alternative modifications and variations as 
fall within the spirit and scope of the appended claims.