Electric motor

Details Electric motor Electric motor

2003-04-14

2004-08-10

Le, Dang (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S0400MM, C310S156530, C310S156010, C310S261100

Reexamination Certificate

active

06774523

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electric motor, and particularly, to a rotor structure of an electric motor.
2. Description of the Background Art
Generally, a brushless direct current (BLDC) motor is made by removing a brush and a commutator from a direct current motor and by installing an electric rectifying device not to generate mechanical and electrical noise. Therefore, motor having various speed from low to high can be fabricated, and a motor having stable rotation torque and long life span with multiple poles can be made.
FIG. 1
is a longitudinal cross-sectional view showing a conventional BLDC motor,
FIG. 2
is a cross-sectional view showing in line II—II, and
FIG. 3
is a brief view showing distribution of magnetic flux density of the motor shown in FIG.
1
.
As shown in
FIG. 1
, the conventional BLDC motor includes a housing body
11
having inner space; a housing
10
having a cover portion
12
for covering an opening portion of the housing body
11
and bearings
13
and
14
installed on center portions thereof; a stator
20
fixedly installed in the housing
10
; a rotor
30
rotatably inserted into the stator
20
; and a rotary shaft
40
fixedly pressed into the rotor
30
and rotatably inserted into the respective bearings
13
,
14
in order to transmit the rotation force of the rotor
30
to outer part.
As shown in
FIG. 2
, the stator
20
includes a stator core
26
including a plurality of teeth
21
protrudingly formed on an inner circumferential surface thereof, slots
22
formed between the respective teeth
21
, and slot opening portions
23
formed between tips
25
which are protrudingly formed on ends of the teeth
21
; and a coil
24
wound on the teeth
21
of the stator core
26
.
The rotor
30
includes a shaft insertion hole
31
, through which the rotary shaft
40
is fixedly press-fitted, on a center portion thereof. In addition, rotor cores
36
on which four magnet insertion slots
32
of ‘V’ shape for fixing two permanent magnets which are symmetric for magnetic center respectively are formed as centering around the rotary shaft
40
in a radial direction are laminated and coupled by a rivet through the rivet hole
35
so that two magnetic centers cross each other in right angle on outer side of the shaft insertion hole
31
.
The permanent magnets
33
are inserted into ends of the magnet insertion slots
32
in pairs to have equal polarity, and installed to have polarity opposite to that of another permanent magnet
33
inserted into adjacent magnet insertion slot
32
.
A recess
34
is formed around the end of the magnet insertion slot
32
in radial direction in order to disperse the magnetic flux density of the permanent magnet
33
.
In the conventional BLDC motor having above structure, when electric source is applied sequentially on the coil
24
wound on respective teeth
21
of the stator
20
by an electric source applying circuit (not shown), the respective teeth
21
have alternating polarity of N and S poles, and the rotor
30
is rotated by magnetic flux between the teeth
21
and the permanent magnet
33
of the rotor
30
which is adjacent to the teeth of the stator
20
.
At that time, interaction between the two permanent magnets
33
inserted in the magnet insertion slots
32
formed on the rotor
30
to have same polarity on both ends thereof and the teeth adjacent thereto will be described in more detail with reference to FIG.
3
.
When the end of the permanent magnet
33
having N polar direction and a tooth
21
having same polar direction, that is, N polar direction, are adjacent to each other on the end of the magnet insertion slot
32
, and magnetic forces are repulsed and repulsive force for pushing each other is generated. In addition, when the end of the permanent magnet
33
having N polar direction and a tooth
21
having opposite polar direction, that is, S polar direction, are adjacent to each other, active magnetic flux (a) is formed and magnetic flux density (b) is concentrated to generate attractive force.
The polarity of the teeth
31
can be changed by the electric source flowing on the coil
24
which is wound on the stator core
26
, and according to the changes, is the repulsive force or the attractive force is applied with the adjacent permanent magnets
33
. In addition, when the repulsive or attractive force is applied toward the tangent direction of the rotor core
36
, the rotor
30
can be rotated smoothly.
However, on a tip portion of the tooth
21
having polar direction opposite to that of the permanent magnet
33
on the end of the magnet insertion slot
32
, the magnetic flux is concentrated and peak flux (c) is generated, and shock force toward radial direction which interrupts the rotation of the rotor
30
is generated.
In addition, the shock force in radial direction generated due to the magnetic flux increase on the tip
25
of the tooth
21
generates vibration when the rotor
30
is rotated, and accordingly, noise due to the vibration is also generated.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide an electric motor having less vibration and noise by restricting generation of shock force generated around a rotor and teeth of a stator.
To achieve the object of the present invention, as embodied and broadly described herein, there is provided an electric motor comprising: a stator including a plurality of teeth and a coil unit wound on the teeth to form rotating magnetic flux by applied electric source; a rotary shaft; and a rotor rotatably installed in the stator, the rotor including a shaft insertion hole so that the rotary shaft can be inserted therethrough and fixed, wherein the rotor includes a plurality of permanent magnet insertion slots of ‘V’ shape formed as centering around the shaft insertion hole in radial direction, and permanent magnets are inserted and fixed into the permanent magnet insertion slots respectively, and a plurality of air gap expanding portions, on which air gaps from the teeth of the stator are expanded, are formed on an outer circumferential surface of the rotor.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.


REFERENCES:
patent: 6049153 (2000-04-01), Nishiyama et al.
patent: 6369480 (2002-04-01), Nishiyama et al.
patent: 6582207 (2003-06-01), Matsumoto et al.

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