Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-01-02
2004-04-27
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S156530
Reexamination Certificate
active
06727627
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to a permanent magnet synchronous motor and, more particularly, to the synchronous motor generally used in a motor-driven compressor in a refrigerating system or an air conditioning system or any other industrially utilized electric appliance.
BACKGROUND ART
A self-starting permanent magnet synchronous motor operates as an inductor motor at the time of starting thereof owing to a starter squirrel cage conductor and as a synchronous motor as rotating magnetic poles created by the permanent magnets are entrained by a rotating magnetic field formed by a stator winding and moving angularly at a synchronous speed upon arrival of the rotor at a speed approaching the synchronous speed. This synchronous motor has an excellent constant speed operating performance and an excellent high efficiency. In particular, various improvement have hitherto been made to a rotor structure of the synchronous motor.
For example, the Japanese Patent Publications No. 59-23179 and No. 63-20105 discloses the prior art rotor structure for the self-starting permanent magnet synchronous motor.
FIG. 6
illustrates the prior art rotor disclosed in the Japanese Patent Publication No. 59-23179. Referring to
FIG. 6
, reference numeral
1
represents a rotor, and reference numeral
2
represents a rotor iron core having a plurality of slots
3
defined therein adjacent an outer periphery thereof. Conductor bars
4
are disposed within those slots
3
and have their opposite ends shortcircuited by respective shortcircuit rings to thereby form a starter squirrel cage conductor. The shortcircuit rings (not shown) are made of an annular electroconductive material disposed on axially opposite ends of the rotor iron core and are connected with the conductor bars
4
. A plurality of magnet retaining holes
5
are provided on an inner side of the conductor bars
4
, with corresponding permanent magnets
6
embedded therein. Reference numeral
7
represents magnetic flux shortcircuit preventive slits that are spaced such a small distance P from the magnet retaining holes
5
that magnetic saturation can take place between the magnet retaining holes
5
and the slits
7
to thereby prevent the magnetic fluxes emanating from the permanent magnets from being shortcircuited between the different magnetic poles.
FIG. 58
illustrates a longitudinal sectional view of the rotor used in the prior art self-starting synchronous motor disclosed in the Japanese Patent Publication No. 63-20105 and
FIG. 59
illustrates a cross-sectional view taken along the line A-A′ in FIG.
58
. Referring to
FIGS. 58 and 59
, reference numeral
11
represents a rotor, and reference numeral
12
represents a rotor iron core made up of a laminate of electromagnetic steel plates. Reference numeral
13
represents conductor bars having their opposite ends connected with respective shortcircuit rings
14
to thereby form a starter squirrel cage conductor. Reference numeral
15
represents permanent magnets embedded in the rotor iron core to form four rotor magnetic poles. Reference numeral
16
represents magnetic flux shortcircuit preventive slits each operable to prevent the magnetic fluxed between the neighboring permanent magnets of the different polarities from being shortcircuited. Reference numeral
17
represents an end plate disposed on each of axially opposite ends of the rotor iron core
2
by means of bolts to avoid any possible separation of the permanent magnets
5
from the rotor iron core
2
.
When the prior art permanent magnet motor of the type provided with the cage conductor is to be used since the conductor bars and the permanent magnets are employed as rotatory drive elements, if the conductor bars and the permanent magnets are incorrectly positioned relative to each other, a force generated from the conductor bars and a force generated by the permanent magnets will be counteracted with each other and, therefore, no efficient rotatory drive will be achieved. Also, the permanent magnet motor provided with such a cage conductor requires a complicated and increased number of manufacturing steps since the permanent magnets and the conductor bars are provided in the rotor.
In view of the foregoing, the present invention is intended to solve those problems inherent in the prior art permanent magnet synchronous motor and is to increase the efficiency and simplify the manufacture of the synchronous motor of the type employing the permanent magnets.
DISLCLOSURE OF INVENTION
To this end, the present invention according to a first aspect thereof provides a synchronous motor which comprises a stator including a stator iron core having a winding wound therearound, said stator iron core having an inner cylindrical surface; a rotor including a rotor iron core and rotatably accommodated while facing the inner cylindrical surface of the stator iron core, said rotor including a plurality of conductor bars accommodated within corresponding slots defined in an outer peripheral portion of the rotor iron core, said conductor bars having their opposite ends shortcircuited by respective shortcircuit rings to form a starter squirrel cage conductor, said rotor having a plurality of magnet retaining slots defined therein at a location on an inner side of the conductor bars; and permanent magnets embedded within the magnet retaining holes in the rotor and defining rotor magnetic poles. In this synchronous motor, the neighboring members of the slots are spaced a distance which is referred to as a slot interval, the slot interval at a location adjacent one end of rotor magnetic poles being smaller than the slot interval at a location adjacent a center point of the rotor magnetic poles.
According to the first aspect of the present invention, the magnetic fluxes emanating from the permanent magnets will hardly leak to the outer peripheral surface of the rotor at a position adjacent opposite ends of the rotor magnetic poles and, instead leak to the outer peripheral surface of the rotor at a position adjacent a center point of the rotor magnetic poles. For this reason, the pattern of distribution of the magnetic fluxes in an air gap between the stator and the rotor represents a generally trapezoidal or sinusoidal waveform such that as compared with the rectangular waveform, the amount of change of the magnetic fluxes per unitary time increases and, therefore, the voltage induced across the winding of the stator can be increased to thereby intensify the rotor magnetic poles. Accordingly, in the practice of the present invention, to secure the required induced voltage, neither is the volume of the permanent magnets increased, nor the permanent magnets having a high residual magnetic flux density are required such as required in the prior art, thus making it possible to provide a high-performance and inexpensive self-starting synchronous motor having a required out-of-step torque and a high efficiency.
If the slot interval at a location spaced from the center point of the rotor magnetic poles in a direction conforming to a direction of rotation of the rotor is chosen to be greater than the slot interval at a location spaced from the center point of the rotor magnetic poles in a direction counter to the direction of rotation of the rotor, although during a loaded operation the maximum value of a distribution, on the rotor surface, of composite magnetic fluxes of the magnetic fluxes from the winding of the stator and the magnetic fluxes from the permanent magnets is positioned on one side conforming to the direction of rotation rather than the center point of the rotor magnetic poles, since the slot interval of the rotor through which the magnetic fluxes at that position pass is increased, the magnetic saturation at that portion can be prevented. Accordingly, the magnetic fluxes emanating from the magnets can be sufficiently taken from the rotor and, therefore, the current across the stator winding can be suppressed to thereby increase the efficiency of the motor.
The present invention according to a second a
Sasaki Kenji
Takimoto Toru
Tamura Teruo
Taniguchi Hideyuki
Uesaka Hiroyuki
Matsushita Electric - Industrial Co., Ltd.
Nguyen Tran
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