Outer rotor type induction motor

Details Outer rotor type induction motor Outer rotor type induction motor

2002-08-08

2004-06-01

Mullins, Burton (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S058000, C310S06000A, C310S180000, C310S266000

Reexamination Certificate

active

06744157

ABSTRACT:

This application claims the benefit of the Korean Application Nos. P2002-7503 and P2002-7510 filed on Feb. 8, 2002, which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an induction motor, and more particularly, to an outer rotor type induction motor having a rotor outside a stator.
2. Discussion of the Related Art
Generally, a motor converts an electric energy into a mechanical energy so as to provide a rotatory power. Motors are mainly divided into AC motors and DC motors, in which an induction motor is a kind of the AC motors.
The induction motors are divided again into an inner rotor type induction motor and an outer rotor type induction motor in accordance with relative positions of rotors and stators. The inner rotor type induction motor is generally applied to a washing machine or the like, and includes the rotor inside the stator.
As the rotor of the inner rotor type induction motor rotates through an inside of the stator, a radius of the rotor is limited so as to produce a less torque per unit volume as well as reduce its utilization of the inner space. Lately, proposed is an induction motor enabling to increase the torque per the same volume in a manner that the rotor is installed outside the stator as well as utilize the inner space of the stator for other usage. Such an induction motor is called an outer rotor type induction motor.
A general structure of the outer rotor type induction motor is explained briefly as follows.
FIG. 1
illustrates a schematic cross-sectional view of a general outer rotor type induction motor.
Referring to
FIG. 1
, an outer rotor type induction motor includes a rotor housing
10
with which a driving shaft
60
is coupled so as to penetrate a center of the rotor housing
10
, a rotor conductor
20
installed at an inner circumference face of the rotor housing
10
so as to constitute a connected circuit, a stator core
30
fixed to a frame
50
so as to maintain a predetermined slit with the rotor conductor
20
inside the rotor housing
10
, and a coil
40
installed at the stator core
30
so as to form a rotatory magnetic field by receiving an AC electric power.
In this case, the driving shaft
60
is coupled with the rotor housing
10
through an insertion hole
11
of the rotor housing
10
, and then penetrates a center of the stator core
30
so as to be supported to rotate by the frame
50
.
Operation of the above-constituted induction motor is schematically explained as follows. The rotatory magnetic field generated from the coil
40
inter-reacts with a current induced on the rotor conductor
20
, thereby generating a torque revolving the rotor conductor
20
in accordance with Fleming's left hand rule.
Yet, in spite of the above-explained advantage, the outer rotor type induction motor has the following disadvantages or problems so as to fail to be used widely.
First, in induction motors including the outer rotor type induction motor, copper loss due to an electric resistance of the coil
40
and core loss due to leakage flux of the stator core
30
are inevitable. The copper and core losses bring about heat considerably. In this case, a temperature inside the induction motor increases so as to increase a resistance of the coil
40
, thereby increasing a power loss. Specifically, if the temperature inside the induction motor is higher than that of an insulation level of the coil
40
, an insulating film formed on a surface of the coil
40
is broken to reduce an endurance of the induction motor severely.
Such a problem becomes severer in the outer rotor type induction motor. As a load torque per volume of the outer rotor type induction motor works more greatly than that of the inner rotor type induction motor, such a load torque results in the temperature increase of the coil
40
directly.
Second, the outer rotor type induction motor has difficulty or weakness in winding the coil
40
on the stator core
30
automatically, whereby automatic mass-production is unavailable so as to increase a product cost.
Generally, there are various methods of winding the coil on the stator core. For instance, an inserting method is carried out by inserting the coil, which is wound previously using a winding machine, into a stator slot automatically. And, a direct winding method is carried out by winding the coil on the stator slot directly. The inserting method us applied to the inner rotor type induction motor. Despite its product cost higher than that of the direct winding method, the inserting method enables the automation so as to be applied to the mass production.
Yet, in order to apply the inserting method to the outer rotor type induction motor, new instruments including a winding machine and the like are required. Hence, the direct winding method is mainly applied to the outer rotor type induction motor. This is because the position and shape of the stator slot of the outer rotor type induction motor are absolutely different from those of the inner rotor type induction motor.
Even if the direct winding method is applied to the outer rotor type induction motor, the automation is impossible.
Specifically, the outer rotor type induction motor, as shown in
FIG. 2
, needs a plurality of poles in order to attain a rotatory power. A count of the poles depends on an arrangement form of the coil. Generally, the widely used coil arrangement form constitutes eight poles using forty-eight stator slots
31
.
Hence, six stator slots
31
are allocated to each of the poles, and the coil is suitably wound on the six stator slots. In this case, the coil is divided into a main winding MC as an operating winding and a supplementary winding SC as a starting winding. For convenience of explanation, random numerals are given to the main winding MC, supplementary winding SC, and stator slot
31
like FIG.
2
. First, a first main winding MC
1
is wound through most outer stator slots
31
a
and
31
f
among the stator slots, and then a second main winding MC
2
is wound through another stator slots
31
b
and
31
e
. And, first and second supplementary windings SC
1
and SC
2
are wound through most inner stator slots
31
c
and
31
d
among the stator slots, respectively. In this case, third and fourth supplementary windings SC
3
and SC
4
are wound together through the stator slots
31
b
and
31
e
through which the second main winding MC
2
is wound, respectively.
In this case, cross-sectional areas(area of a space in which the coil is wound) of the stator slots
31
are equal to each other, there is difficulty in winding the coil automatically. As the stator slot on which another coil is wound exists between the stator lots where a random coil is wound, spaces in which the coils are wound are overlapped with each other so as to bring about a competition between the coils. For instance, four stator slots
31
b
,
31
c
,
31
d
, and
31
e
are formed between the most outer stator slots
31
a
and
31
f
on which the first main winding MC
1
is wound. In this case, the first main winding MC
1
comes into competition with the second main winding MC
2
and first to fourth supplementary windings SC
1
to SC
4
wound on the rest stator slots
31
b
,
31
c
,
31
d
, and
31
e
in the same space.
Unfortunately, it is substantially impossible to wind the coil automatically to bring about an automated mass production, thereby increasing a product cost. Besides, it is able to prevent the coils from competing each other in the winding space by securing the cross-sectional area of the stator slot
31
sufficiently, whereby a size of the stator core has to be increased.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to an outer rotor type induction motor that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an outer rotor type induction motor enabling to improve a reliance and an endurance of a product as well as reduce its power consumption by cooling a coi

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