Motor with permanent magnet

Details Motor with permanent magnet Motor with permanent magnet

2002-04-08

2003-06-24

Ramirez, Nestor (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S257000, C310S256000, C310S256000, C310S156030

Reexamination Certificate

active

06583531

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a motor with permanent magnets; and the motor can realize an operation of high efficiency and low noise. More particularly, a uniquely shaped air gap between teeth of a stator and a rotor of the motor lies at the heart of the present invention.
BACKGROUND ART
FIG. 8
is a cross section of a conventional motor with permanent magnets.
In
FIG. 8
, stator
580
comprises the following elements:
six units including six teeth
581
with windings (not shown) and six yokes
582
connected to respective teeth
581
; and these six units being coupled with each other at junctions
583
thereby forming a ring-shaped stator.
Wires can be wound on respective teeth
581
independently, so that the normal windings on teeth are achievable. As a result, a winding in a high density with less wire-wound-resistance is obtainable.
Rotor
590
comprises the following elements:
rotor core
591
shaped in an approx. cylinder;
shaft
594
disposed at the center of rotor core
591
;
four pieces of permanent magnets
592
mounted on an outer wall of rotor core
591
; and
tube
593
made of e.g. thin stainless steel and covering permanent magnets
592
for preventing the magnets from scattering.
In such a conventional motor as discussed above, the air gaps between respective teeth
581
and rotor
590
have approx. the same width as shown in FIG.
8
.
Rotating magnetic field, produced by electric current travelling through the windings of stator
580
, rotates rotor
590
on shaft
594
. The rotating magnetic field is produced in this way: Adjacent teeth have different phases with each other and the stator's windings are thus three-phase-windings. In a regular operation, a driving circuit detects a position of the rotor and switches phases to be powered sequentially. In this case, each phase is powered every
120
electric angle, and yet one phase always remains non-powered, so that the rotating magnetic field is produced.
In the conventional motor with permanent magnets discussed above, opposite magnetic fields are produced between the adjacent teeth of active two pairs of windings out of six teeth. Therefore, magnetic flux at slot-open-section
584
is vulnerable to short-circuit. The slot-open-section is a clearance between the tips of the adjacent two teeth, and an opening section of a slot formed by the adjacent two teeth.
FIG. 9
shows Maxwell's stress distribution produced at the air gap in the motor discussed above. The arrow marks show. the stress distribution. The arrow marks indicate the distribution of forces which the magnetic flux at the air gap supplies to the stator. When permanent magnet
5929
is polarized S pole, electric current travels through the windings so that tooth
5811
is magnetized S pole and tooth
5812
is magnetized N pole. Then rotor
590
rotates in rotating direction R as shown in FIG.
8
. In this case, strong attraction is produced between magnet
5929
(S) and tooth
5812
(N), thus stress
587
produced therebetween becomes greater discontinuously.
FIG. 10
shows the way the magnetic-flux-density at the air gap around a slot-open in the motor changes with respect to a rotational angle of the rotor. In other words,
FIG. 10
illustrates the time-based change of the magnetic-flux-density at the air gap around slot-open
584
in FIG.
8
. In
FIG. 10
, the X-axis represents a rotational angle (mechanical angle) of rotor
590
in rotating direction R. When the magnetic-flux-density takes positive values, the rotor is polarized N pole, and when the density takes negative values, the rotor is S pole. The magnetic-flux-density seems to vary smooth; however, it rises sharply in 20-degree range on rotational angle 45-degree. This sharp change corresponds to stress
587
shown in
FIG. 9
, where stress
587
becomes large discontinuously, and this causes vibrations and noises in the motor operation.
SUMMARY OF THE INVENTION
The present invention addresses the problems discussed above, and aims to provide a motor having air-gap, which is situated between the teeth of the stator and the rotor, so that noise lowers and withstanding force against demagnetization grows.
The motor of the present invention comprises the following elements:
(a) a stator including a plurality of teeth on which wires are wound and yokes coupling the teeth; and
(b) a rotor having permanent magnets and facing to the stator via an air-gap.
A part of the air-gap at rotating tail of the teeth facing to the rotor is formed to be larger than other parts of the air-gap. This structure prevents the magnetic-flux-density at the air-gap from sharply rising, thereby lowering vibrations and noises.


REFERENCES:
patent: 4730136 (1988-03-01), Muller
patent: 5038065 (1991-08-01), Matsubayashi et al.
patent: 5041749 (1991-08-01), Gaser
patent: 5148090 (1992-09-01), Oku et al.
patent: 5170083 (1992-12-01), Burgbacher
patent: 5331245 (1994-07-01), Burgbacher et al.
patent: RE35763 (1998-04-01), Burgbacher
patent: 5757100 (1998-05-01), Burgbacher
patent: 6049153 (2000-04-01), Nishimaya et al.
patent: RE37576 (2002-03-01), Stephens et al.
patent: 555100 (1932-07-01), None
patent: 0 564 759 (1993-10-01), None
patent: 1523356 (1968-08-01), None
patent: 09103062 (1997-04-01), None

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