Induction motor

Details Induction motor Induction motor

2003-04-15

2004-11-16

Ponomarenko, Nicholas (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S184000, C310S198000

Reexamination Certificate

active

06819026

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a radial-air-gap induction motor used as a fan motor of an air conditioner, particularly to an induction motor having two stators and provided with a two radial air gaps constituted by setting a rotor between the stators.
BACKGROUND ART
Most induction motors respectively use the inner rotor type constituted by setting one rotor at the inside of one stator for generating a rotating magnetic field. The stator is provided with windings in order to generate a rotating magnetic field and the rotor is provided with case windings for generating an induced current.
In the case of the above induction motor, when setting the rotor in the rotating magnetic field of the stator, an induced current circulates through the case windings of the rotor, a rotating torque works on the case windings due to the mutual action between the rotating magnetic field and the induced current and thereby, the rotor rotates. This type of the induction motor is frequently used for electrical home appliances and industrial machines from the viewpoints of simplicity and economical efficiency.
In the case of a conventional induction motor, however, a loss tends to increase and an efficiency tends to deteriorate for an output as the motor is further decreased in size and moreover, the trend of the efficiency deterioration becomes stronger as the number of poles of the motor increases.
The relation shown by the following expression (1) is present between efficiency, loss, output, and input.
Efficiency=Output/input=Output/output+Loss  (1)
Therefore, it is found that a loss should be decreased in order to improve an efficiency. The loss of an induction motor includes the following.
<1> Primary copper loss (Copper loss; Stator winding resistance loss)
<2> Secondary copper loss (Rotor winding resistance loss)
<3> Iron loss (Core loss; Hysteresis loss)
<4> Iron loss (Eddy current loss)
<5> Mechanical loss (Bearing loss or windage loss)
<6> Stray load loss
The primary copper loss in <1> and the secondary copper loss in <2> account for a large ratio among the above <1> to <6>. To reduce these copper losses of a conventional induction motor, it is necessary to use one of a method for reducing a resistance loss by increasing a stator core in size and a groove (slot) area and coiling a winging having a large wire diameter and a method for increasing the outer diameter of a rotor core so that the same torque can be output even by a small induced current. However, these methods are not preferable because the material cost is greatly increased.
In general, the output equation of a motor is shown by the following expression (2).
Output=
K
1
·D
2
·L·Bm·Ac·n
  (2)
In the above expression, K
1
denotes a constant, D denotes the diameter of a radial air gap, L denotes the length of a core, Bm denotes the average magnetic-flux density of an air gap, Ac denotes the number of ampere conductors, and n denotes a rotating speed.
In the case of an induction motor, the average magnetic-flux density Bm of an air gap is almost proportional to the number of ampere conductors Ac. Therefore, the above expression (2) can be shown as the following expression (3).
Output=
K
2
·D
2
·L·Bm
2
·n
  (3)
In the above expression, K
2
is a constant.
Then, the relation between a loss and the average magnetic-flux density Bm of an air gap is studied below. A current I is almost proportional to a maximum magnetic-flux density B. The number of ampere conductors Ac is almost proportional to the current I and the average magnetic-flux density Bm of an air gap is almost proportional to the maximum magnetic-flux density B. Therefore, it can be considered that the primary copper loss (current I
2
·winding resistance) in the above <1> almost proportional to Bm
2
.
Moreover, the secondary copper loss in the above <2> is equal to (secondary current circulating through a rotor winding)·secondary resistance and the secondary current is almost proportional to Bm. Therefore, it can be said that the secondary copper loss in the above <2> is almost proportional to Bm
2
.
It is publicly known that the iron loss (hysteresis loss) in the above <3> and the iron loss (eddy current loss) in the above <4> are almost proportional to B
2
, that is, Bm
2
. Because it is estimated that the mechanical loss (bearing loss or windage loss) in the above <5> and the stray load loss in the above <6> account for a small rate in the total loss, it can be said that the total loss is almost proportional to Bm
2
.
To greatly improve an efficiency, it is necessary to minimize losses. Because a loss is almost proportional to the square of the average magnetic-flux density Bm (Bm
2
) of an air gap, it is necessary to greatly reduce Bm
2
in order to greatly reduce the loss. However, because by reducing Bm
2
, an output is also reduced proportionally to Bm
2
, it is necessary to use means for compensating the output.
As a method for realizing the above mentioned, it is possible to keep an output constant because (Bm
2
)×(D
2
·L) becomes constant by increasing the square of (diameter D of radial air gap)×core length L by a value equivalent to the decrease of Bm
2
. However, it is uneconomic to increase (D
2
·L) in a conventional induction motor because a core size (constitution) increases.
Therefore, it is a problem of the present invention to greatly improve the efficiency of an induction motor without increasing the core size (constitution).
SUMMARY OF THE INVENTION
To solve the above problem, the present invention uses an induction motor having a radial air gap, which is constituted so as to have a two air gaps and in which windings for generating a rotating magnetic field for the above rotor is set to the above outer and inner stators, and squirrel-cage windings are set to the rotor.
Thus, by forming the radial air gaps and maximizing the diameter of each air gap, it is possible to greatly increase (D
2
·L). Therefore, it is also possible to greatly reduce Bm
2
and thereby greatly reduce losses. Therefore, it is possible to improve an efficiency without increasing the core size (constitution). The output equation when forming the radial air gaps is shown by the following expression (4).
Output=
K
2
·(
Do
2
+Di
2
)·
L·Bm
2
·n
  (4)
In the above expression, Do denotes the diameter of the outer radial air gap and Di denotes the diameter of the inner radial air gap.
It is preferable that the number of slots of the outer stator is equal to or different from the number of slots of the inner stator and the number of slots of the above rotor is equal to prime number×2 or prime number×4. Thereby, a squirrel-cage winding rotor becomes suitable for an induction motor.
It is preferable to make the pitch between windings applied to the inside of the above outer stator equal to or different from the pitch between windings applied to the outside of the above inner stator. Thereby, an induction motor suitable for a purpose is realized.
According to the present invention, it is possible to realize a capacitor induction motor in which an induced current circulates through the squirrel-cage windings of a rotor in accordance with a rotating magnetic field generated in each stator by applying the same numbers of or different numbers of slots to the above outer and inner stators, relatively shifting a spatial phase angle by &pgr;/2 in terms of an electrical angle, applying main windings and auxiliary windings to the teeth formed at the inside of the outer stator in the form of a concentrated windings, applying a main windings and an auxiliary windings to the grooves formed at the outside of the inner stator in the form of a distributed winding or concentrated winding, and generating a rotating magnetic field in each stator.
In
FIGS. 4
to
6
, according to the present invention, a main windings and auxiliary windings are alternately applied to teeth constituti

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