Electricity: motive power systems – Synchronous motor systems – Armature winding circuits
Reexamination Certificate
2001-03-21
2002-07-23
Mullins, Burton S. (Department: 2834)
Electricity: motive power systems
Synchronous motor systems
Armature winding circuits
C318S720000, C318S700000, C310S06800R
Reexamination Certificate
active
06424114
ABSTRACT:
FIELD OF TECHNOLOGY
The present invention relates to a synchronous motor.
BACKGROUND TECHNOLOGY
These days, office automation equipments, for example, have DC or AC fan motors for cooling. Especially, in the case of high rotational speed, AC fan motors having two or four magnetic poles are preferably employed.
The inventor invented synchronous motors (see JP7-232268, JP8106929, etc.), each of which has armature coils and a rectifying circuit, which includes a diode, a brush, a commutator, etc. and is connected to the coils; and each of the motors rectifies AC current, which is supplied from an AC power source, and starts to rotate a permanent magnet rotor, as a DC motor, until its rotational speed reaches near synchronous speed, then the commutator is mechanically disconnected from the rectifying circuit so as to transfer to synchronous operation with the AC power source.
A two-magnetic pole synchronous motor has rotational speed of 3,000 rpm (50 Hz) or 3,600 rpm (60 Hz), small size, high working efficiency and applicability, so it is preferably used as an AC fan motor, etc.
An example of an outer rotor-type two-magnetic pole synchronous motor is shown in
FIGS. 17 and 18
. A commutator
101
is capable of moving in an axial direction of an output shaft
102
so as to mechanically changing operational state from a start operation to a synchronous operation. A ring-shaped permanent magnet rotor (not shown), in which two magnetic poles are provided with angular separation of 180°, is coaxial to the commutator
101
and attached to the output shaft
102
. The permanent magnet rotor is started by magnetic repulsion, which is occurred when electric current flows through armature coils
103
. An electric conductive slide ring
104
, whose central angle is less than 180°, is provided to an outer circumferential face of the commutator
101
.
When the rotational speed of the permanent magnet rotor reaches near synchronous speed, the commutator
102
is moved in the axial direction, by centrifugal force of a weight not shown, against elastic force of a coil spring (not shown). With this action, a switch
107
electrically disconnects a rectifying circuit
106
from a single-phase AC power source
105
and electrically connects the coils
103
to the power source
105
.
The coils
3
are two coil segments: an A-coil and a B-coil. The A-coil and the B-coil are formed by winding a wire round a bobbin, not shown, in a prescribed direction with prescribed turns. Power supply brushes
108
a
and
108
b
contact the slide ring
104
, which is provided on the outer circumferential face of the commutator
101
, so as to alternately supply electric power, so their phases are mutually shifted 180°. A-power receiving brushes
109
a
and
109
b
are used to supply the electric power to the A-coil; B-power receiving brushes
110
a
and
110
b
are used to supply the electric power to the B-coil. At least one of the A- and the B-power receiving brushes
109
a,
109
b,
110
a
and
110
b
contacts the slide ring
104
so as to receive the electric power, so phases of the pairs are mutually shifted 180°. Diodes
111
a
and
111
b
are connected to the A-power receiving brushes
109
a
and
109
b
and diodes
112
a
and
112
b
are connected to the B-power receiving brushes
110
a
and
110
b
so as to half-wave-rectify the AC current from the AC power source
105
and supply the half-wave-rectified current to the A-coil and the B-coil (see FIG.
17
).
The power supply brushes
108
a,
108
b,
the A-power receiving brushes
109
a
and
109
b
and the B-power receiving brushes
110
a
and
110
b
are respectively biased radially inward by electrically conductive plate springs
114
a,
114
b,
115
a,
115
b,
116
a
and
116
b,
which are provided to a housing
113
(see FIG.
18
), so that they can contact the slide ring
104
(see FIG.
17
).
The AC current supplied from the single-phase AC power source
105
is rectified by the rectifying circuit
106
, which is connected to the coils
103
, so that the permanent magnet rotor is magnetically started, as the DC motor, until its rotational speed reaches near the synchronous speed. Upon reaching near the synchronous speed, the commutator
101
is mechanically disconnected from the rectifying circuit
106
, and the switch
107
is turned so as to short the AC power source
105
and the coils
103
so as to synchronously rotate the permanent magnet rotor
103
. Note that, symbols C
1
, C
2
and C
3
stand for capacitors for absorbing surge current.
In the synchronous motors disclosed in JP7-232268, JP8-106929, etc., the permanent magnet rotor is started, as the DC motor, until its rotational speed reaches near the synchronous speed, then the commutator
101
is mechanically moved in the axial direction so as to electrically disconnect from the rectifying circuit
106
and turn the switch
107
, so that power consumption can be highly improved in comparison with conventional induction motors, but number of parts must be increased, the structure must be complex and size of the motor cannot be smaller.
The rotor should be transferred from the start operation to the synchronous operation by one action, but the commutator is not always moved smoothly and power swing is sometimes occurred by overload, so that the rotor must be restarted and retransferred, namely the transition of the operation cannot be securely executed.
Further, a plurality of brushes and the slide ring repeatedly contact, so they are abraded and cannot fully contact, especially, in the case of high power motors whose power is 50 W or more, the current is apt to spark when the current direction is changed during the start operation, so safety and reliable synchronous motors are required.
DISCLOSURE OF THE INVENTION
An object of the present invention is to solve the above described problems of the conventional synchronous motors and to provide a small-sized reliable synchronous motor, whose energy consumption is low and which can securely transfer from the start operation to the synchronous operation.
To achieve the object, the present invention has following structures.
Namely, the synchronous motor of a first structure comprises: a permanent magnet rotor being rotatably attached in a housing proper and rotating about an output shaft; and a stator including coils, which are wound round a stator core, characterized by: the coils including an A-coil segment and a B-coil segment, which are connected in series; first measuring means for measuring rotational speed of the permanent magnet rotor and positions of magnetic poles thereof; second measuring means for measuring frequency of an AC power source; a start operation circuit rectifying alternate current, which is supplied from the AC power source, with a rectifying bridge circuit and changing the direction of the rectified current, which flows through the A-coil of the coils, according to rotational angle of the permanent magnet rotor by controlling switching means so as to start the permanent magnet rotor as a DC brushless motor; a synchronous operation circuit shorting the AC power source and the A- and the B-coils so as to synchronously rotate the permanent magnet rotor as an AC synchronous motor; switches being provided between the AC power source and the coils and switching the connection to the synchronous operation circuit; and control means turning off the switches to disconnect the synchronous operation circuit and controlling the switching means during the start operation, starting with suppressing input of inverted minus side of the AC power source, which is full-wave-rectified and flows through the A-coil of the coils via the rectifying bridge circuit, so as to make the current application range of the minus side shorter than that of the plus side, turning off the switching means and turning on the switches when the rotational speed of the permanent magnet rotor, which is measured by the first measuring means, reaches near synchronous speed with respect to the frequency of the power source, which is measured by the second measuring me
Jordan and Hamburg LLP
Mullins Burton S.
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