Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-07-26
2001-04-17
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S216006, C310S261100
Reexamination Certificate
active
06218753
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a driving motor used in air conditioners, industrial apparatuses and electric bicycles. More particularly, it relates to a motor structure that employs a rotor core having an interior permanent magnet, and utilizes not only magnet torque but also reluctance torque so that a higher efficiency motor can be realized.
BACKGROUND OF THE INVENTION
A high efficiency motor, which can utilize magnet torque as well as reluctance torque by burying interior magnets within a rotor core, is well known in the market, one example is disclosed in the Japanese Patent Application Unexamined Publication No. H08-331823.
FIG. 18
is a cross section illustrating this kind of conventional motor.
In
FIG. 18
, stator
401
comprises a plurality of teeth
403
and yoke
405
which connects roots of the plural teeth, and stator
401
is shaped as a ring. A plurality of slots
407
formed between teeth
403
are wound in a three-phase winding manner.
Rotor
410
is substantially coaxial with stator
401
and is shaped substantially as a cylinder, and faces an inner wall of stator
401
via an annular space. Rotor
410
has four rotor poles, and is supported by a bearing (not shown) so that rotor
410
can rotate on shaft
421
. Four slits
413
bored through axially and disposed at equal intervals along a rotational direction of rotor core
411
are provided on rotor
410
, and plate-like permanent magnet
415
is inserted into each slit. A terminal plate (not shown) is disposed on each axial end of rotor core
411
to secure permanent magnet
415
. The terminal plate is fixed on the end face by riveting pin
425
through hole
423
, whereby the permanent magnet
415
is fixed into rotor core
411
. An outer wall of rotor
410
has notches
419
at boundary areas between the respective rotor poles, and both of longitudinal ends of permanent magnet
415
are adjacent to respective notches
419
. An electric current runs through the stator coil to create a rotating magnetic field. Then, the rotor poles attract/repel teeth
403
of stator
401
, thereby spinning rotor
410
.
In the above structure, the following relation is established between inductances Ld and Lq: Ld<Lq
where Ld is an inductance along “d” axis which crosses the rotor pole at right angles, and
Lq is an inductance along “q” axis extending through the boundary area between the rotor poles.
In general, motor torque “T” is expressed by the following equation:
T=Pn{&psgr;a•I•cos&bgr;+0.5(Lq−Ld)I
2
•sin2&bgr;}
where, Pn: a number of paired rotor poles,
&psgr;a: interlinkage magnetic flux
I: stator coil current
&bgr;: leading phase angle of the current I (electrical angle)
In the equation discussed above, the first term represents magnet torque, and the second represents reluctance torque. Since the relation of Ld<Lq is satisfied, a winding current is so controlled to advance the phase of the winding current “I” with regard to respective induced voltage generated in each phase winding, thereby &bgr; becomes greater than zero (&bgr;>0), and the reluctance torque is generated. When &bgr; is set at a predetermined value, the greater torque “T” can be produced with a same current than the case where only the magnet torque is available.
However, according to the above structure, since steel section
417
having high permeability exists between slit
413
and notch
419
, magnetic flux at the end of permanent magnet
415
runs through magnetic path
430
of steel section
417
. The magnetic flux is thus short-circuited as shown in
FIG. 18
, although it should have reached stator
401
and contributed to torque production. In other words, the magnetic flux decreases by the short-circuited amount, thereby lowering a motor efficiency. Further, the magnetic flux resulted from short-circuited increases cogging torque, which increases noises and vibrations of the motor.
A motor employing another type of interior permanent magnets is disclosed in the Japanese Patent Application Unexamined Publication No. H08-331783 as shown in FIG.
19
. This prior art, different from the conventional motor discussed above, has no notches on the outer wall, and a distributed winding method is employed on stators.
In
FIG. 19
, rotor
503
has four sets of interior permanent magnets
501
and
502
in rotor core
507
made of electromagnetic stacked steel sheets. Magnets
501
and
502
are placed on each pole in a radial direction with a space. Each set of magnets
501
and
502
are places such that “S” pole and “N” pole are adjacent to each other. Magnets
501
and
502
forming a layer structure are placed such that the outer sides of respective outer magnets
501
facing the outer rim of rotor
503
have the same polarity as the outer sides of respective inner magnets
502
. Magnets
501
and
502
are shaped as arcs and show their hills toward the rotor center, and the two magnets in the layer structure form substantially concentric circles and lie in parallel. A space between the two magnets is substantially constant.
Rotor
503
as defined above is rotated by composite torque of magnet torque and reluctance torque: i.e. the magnet torque is generated by the relation between the magnet field of magnets
501
and
502
and rotating magnetic field produced by the current running through a group of coils
509
striding over a predetermined number of teeth
506
defined by broken lines
517
, on the other hand, the reluctance torque is generated by magnetic paths formed by the rotating magnetic field and appearing between magnets
501
and
502
as well as on the surface of rotor
503
. The reluctance torque is thus utilized, thereby realizing a higher efficiency motor than the motor using only magnet torque.
Among such motors as employing interior permanent magnets, another idea is carried out not only to increase efficiency but also to downsize the motor, i.e. a concentrated winding method is practiced on the teeth of stator in a higher density.
However, in conventional motor with the concentrated winding on the teeth, an adjacent magnetic pole turns to an opposite pole when the motor is powered with three-phase 120° current and winding volume for one pole and one phase is concentrated on one tooth. Magnetizing force is thus as strong as twice of the motor with the distributed winding, and therefore magnetic flux runs between the adjacent teeth, which demagnetizes the interior permanent magnets.
SUMMARY OF THE INVENTION
The present invention addresses the problems discussed above and aims to provide a motor with stable driving torque. A motor of the present invention having interior permanent magnets comprises the following elements:
(a) a stator core having a plurality of teeth and a yoke connecting the teeth;
(b) concentrated windings on the teeth;
(c) a rotor having interior permanent magnets;
and the rotor with the interior permanent magnets comprises the following elements:
(c-1) a rotor core having a plurality of slits extending closely to a circumference of the rotor;
(c-2) permanent magnets positioned in the slits;
(c-3) non-magnetic section provided between the circumference of the rotor-core and the ends of respective magnets.
This construction allows magnetic flux due to demagnetizing field to run through the non-magnetic-sections, whereby the demagnetization at the ends of permanent magnets can be restrained. Part of the slit close to the circumference of the rotor-core is particularly subjected to demagnetization; however, the magnetic flux from the teeth due to demagnetization hardly affects the permanent magnets because of the presence of non-magnetic-section. The motor of the present invention thus can restrain the demagnetization at the ends of respective magnets, thereby supplying stable driving torque.
Another motor having a different structure is available. This motor aims to reduce noises and vibrations at spinning. The motor comprises the following elements:
(a) stator core having a plurality of teeth and a yoke connecting the teeth;
(b) win
Asano Yoshinari
Shinto Masayuki
Yamamoto Toshio
Dinh Le Dang
Matsushita Electric Industrial C., Ltd.
Ramirez Nestor
Rossi & Associates
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