Electricity: motive power systems – Synchronous motor systems
Reexamination Certificate
1999-07-22
2001-03-20
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Synchronous motor systems
C318S705000, C318S712000, C318S714000, C310S156030
Reexamination Certificate
active
06204626
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. HEI 10-243955 filed on Aug. 28, 1998 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a driving method and a driving device for a motor, and more particularly, to a driving method and a driving device for a concentrated winding synchronous motor.
2. Description of the Related Art
FIGS. 5A
,
5
B and
5
C illustrate partially sectional views of a concentrated winding synchronous motor. Referring to the drawings, a rotor
32
shown in
FIG. 5B
has been rotated counterclockwise at 7.5 from the state of the rotor shown in
FIG. 5A
as a reference, and the rotor
32
shown in
FIG. 5C
has been rotated counterclockwise at
15
from the reference state shown in FIG.
5
A.
In the concentrated winding synchronous motor shown in the drawings, a stator
35
having a plurality of teeth
34
a
through
34
f
is fitted inside a cylindrical case
30
. In the case of the motor shown in the drawings, the coil of the stator
35
is of the concentrated winding type, and each of the teeth
34
is wound with a coil of either phase U, V, or W.
The rotor
32
is pivotally supported inside the stator
35
. Radially magnetized permanent magnets are attached to the outer surface of the rotor
32
. These permanent magnets function as magnetic poles
36
a
through
36
d
of the rotor
32
. In this type of motor, three phase alternating current is supplied to the coils of the teeth
34
to form a rotating magnetic field in the stator
35
, and the repeated cycle of attraction and repulsion between the respective magnetic poles
36
and the teeth
34
serves to drive the rotor
32
at a predetermined torque.
Adoption of such concentrated winding can simplify the manufacturing process of the synchronous motor owing to the easy installation of the coil compared with the distributed winding (wrapping) in which the coil is applied to wind about one or more teeth
34
.
However, applying the coil of concentrated winding type to the teeth
34
may fail to efficiently obtain the required torque.
FIG. 6
illustrates how the aforementioned problem arises. The upper side of
FIG. 6A
shows the portion interposed between the magnetic poles
36
b
,
36
c
and the teeth
34
b
through
34
e
opposite thereto in a rotating direction in FIG.
5
A. The lower side of
FIG. 6A
shows the magnetic field formed by the stator
35
at the position of the rotor
32
.
FIGS. 6B and 6C
likewise show each of the portions interposed between the magnetic poles
36
b
,
36
c
and the teeth
34
b
through
34
e
opposite thereto illustrated in
FIGS. 5B and 5C
, and the magnetic field formed by the stator
35
at the position of the rotor
32
.
As indicated in
FIG. 6A
, the S pole magnetic field (inward magnetic field) formed by the tooth
34
b
and the N pole magnetic field (outward magnetic field) formed by the tooth
34
c
coexist separately left and right on the surface facing the magnetic pole
36
b
. Similarly the N pole magnetic field formed by the tooth
34
c
and the S pole magnetic field formed by the tooth
34
e
coexist left and right on the surface facing the magnetic pole
36
c
. Therefore, when the rotor
32
is at the position illustrated in
FIG. 6A
or
FIG. 5A
, the magnetic poles
36
b
and
36
c
are attracted by the respective destination teeth
34
c
and
34
e
as well as being repelled by the respective teeth
34
b
and
34
c
behind thereof, thereby enabling the rotor
32
to generate torque efficiently.
In the state shown in
FIG. 6C
, the magnetic poles
36
b
and
36
c
are likewise attracted by the respective destination teeth
34
d
and
34
e
as well as being repelled by the respective teeth
34
b
and
34
d
behind thereof, thereby enabling the rotor
32
to generate the torque efficiently.
However, a state shown in
FIG. 6B
exists in the process proceeding from the state of
FIG. 6A
to that of FIG.
6
C. That is, since the current supplied to each phase has a sinusoidal wave, the generated N pole magnetic field opposing the magnetic pole
36
b
becomes relatively weak compared with the state shown in
FIG. 6A
, and the generated N magnetic field opposing the magnetic pole
36
c
becomes relatively strong as compared with the state shown in FIG.
6
A. In this state, a part of the magnetic fields formed on the surface facing the magnetic poles
36
b
and
36
c
may fail to contribute to generation of the torque, and act to reduce the torque generated. In the case of the magnetic pole
36
b
, as shown by arrow A in
FIG. 6B
, a portion of N pole magnetic field generated by the tooth
34
c
exists behind a centerline
38
b
of the magnetic pole
36
b
, that is, at the side reverse to the rotating direction. Therefore the magnetic pole
36
b
is pulled back in a direction reverse to the rotating direction. The aforementioned phenomenon applies to the magnetic pole
36
c
. As indicated by arrow B in
FIG. 6B
, a portion of the N pole magnetic field generated by the tooth
34
d
exists at a forward side, in the rotating direction, of a centerline
38
c
of the magnetic pole
36
c
. This may push back the magnetic pole
36
c
in a direction reverse to the rotating direction.
Accordingly, when adopting the concentrated winding for the synchronous motor coil, depending on the position of the rotating rotor
32
, a portion of each phase current supplied to the coil of the stator
35
of the synchronous motor may serve to impede generation of torque. As a result, the rotating torque is not efficiently obtained.
SUMMARY OF THE INVENTION
The present invention has been made in view of the aforementioned drawbacks, and it is the object of the present invention to provide a motor driving method and a motor driving device capable of generating a larger torque upon the supply of the same electric current to the stator coil of the concentrated winding synchronous motor.
Therefore, in the present invention, a correction is executed by decreasing the alternating current supplied to the coil wound around the teeth if a portion of the magnetic field generated by the teeth of the stator produces magnetism in a direction opposite of a direction of rotation of a rotor with respect to the pole of the closest rotor. When using the electric current supplied to the coil so as to impede generation of the torque, the amount of current supplied is limited to improve torque generating efficiency.
The present invention also executes a correction by decreasing the alternating current supplied to the coil of a first tooth for a predetermined first period included in the time taken for a pole of the rotor to move from a position opposing the first tooth of the stator to a bridge portion between the first tooth and an adjacent second tooth. It may also execute a correction by decreasing the alternating current to be supplied to the coil of a second tooth for a predetermined second period included in the time taken for the pole of the rotor to move from the bridge portion between the first tooth and the adjacent second tooth of the stator to a position opposing the second tooth. In this way, the current is supplied to the coil of the first tooth for a predetermined period, thus impeding generation of the torque. By limiting the supply of such current, the torque generating efficiency can be improved.
REFERENCES:
patent: 3999108 (1976-12-01), Tanikoshi
patent: 4743825 (1988-05-01), Nashiki
patent: 6034460 (2000-05-01), Tajima et al.
patent: 62-141998 (1987-06-01), None
patent: 8-331884 (1996-12-01), None
Kenyon & Kenyon
Leykin Rita
Nappi Robert E.
Toyota Jidosha & Kabushiki Kaisha
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