Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1998-11-13
2001-01-09
Mullins, Burton (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S156030, C310S06700R, C310S049540
Reexamination Certificate
active
06172442
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a disk-type brushless single-phase DC motor, and more particularly to a disk-type brushless single-phase DC motor including an armature coil attached to a stator yoke of a stator in such a fashion that it faces the lower surface of a rotor magnet having a plurality of alternating N and S poles, the armature coil having a closed loop structure provided with a plurality of uniformly spaced apexes, and cogging generating protrusions of a miniature size protruded from the stator yoke at positions spaced in a rotation direction of the rotor magnet from respective apexes of the armature coil by an angle corresponding to ¼ of an angular width of one pole, thereby being capable of achieving an improvement in drive efficiency.
2. Description of the Prior Art
Generally, disk-type brushless single-phase DC motors are used in miniature fan motors for simple rotating appliances requiring no precise rotation, for example, office appliances such as computers.
Referring to
FIG. 8
a disk-type brushless single-phase DC motor is illustrated which includes a housing
100
constituting a lower portion of the motor and serving to support elements of the motor, and a rotor
300
constituting an upper portion of the motor and arranged over the housing
100
. The rotor
300
is rotatably coupled to the housing
100
by means of a shaft
200
.
A multipolar rotor magnet
310
is mounted on the lower surface of the rotor
300
within the rotor
300
. The multipolar rotor magnet
310
has a plurality of alternating N and S poles. The upper end of the shaft
200
is fixedly mounted to the central portion of the rotor
300
. The shaft
200
extends downwardly through a bearing housing
110
upwardly protruded from the central portion of the housing
100
in such a fashion that it is rotatably supported by bearings mounted in the bearing housing
110
. The upper end of the bearing housing
110
has a stepped structure in order to fixedly mount a stator
400
thereon.
The stator
400
mainly includes a printed circuit board
410
, a stator yoke
420
laid on the printed circuit board
410
, and armature coils
430
attached to the upper surface of the stator yoke
420
by means of an adhesive.
The driving of the disk-type brushless single-phase DC motor having the above mentioned configuration is achieved by a rotation of the rotor
300
carried out by an electromagnetic force generated between the armature coils
430
of the stator
400
and the rotor magnet
310
.
This will be described in more detail. When single-phase current is supplied to the armature coils
430
via the printed circuit board
410
, an electromagnetic force is generated in accordance with an interaction between the armature coils
430
and the rotor magnet
310
, thereby generating a drive force. By this drive force, the rotor
300
rotates.
In this case, a coil torque
600
is generated between the armature coils
430
and the rotor magnet
310
by the electromagnetic force, as shown in FIG.
9
. The coil torque exhibits a maximum value at the middle portion of each pole in the rotor magnet
310
and decreases gradually as the pole extends from the middle portion thereof to each lateral end thereof. The coil torque becomes zero at each lateral end of each pole, thereby causing the rotor
300
to stop.
The point, where the coil torque is zero, is called a “dead point”. A cogging generating means is provided for a magnetic start-up at such a dead point.
Such a cogging generating means provides a cogging force serving as a load against the coil torque. Such a cogging force is adapted to increase the minimum coil torque while decreasing the maximum coil torque, thereby obtaining a substantially uniform torque. That is, a cogging torque, which has a waveform
700
in
FIG. 9
, is generated simultaneously with the generation of the coil torque, which has a waveform
600
in
FIG. 9
, thereby obtaining an ideal resultant torque which has a waveform
800
in FIG.
9
. The cogging torque, which serves as a load against the coil torque, has an output level inversely proportional to the output level of the coil torque, thereby reducing the variation in the resultant torque. As a result, the motor can drive stably.
A variety of motors provided with such a cogging means have been proposed in, for example, U.S. Pat. No. 4,620,139, U.S. Pat. No. 4,757,222, and Japanese Patent Publication No. Heisei 7-213041. The cogging means disclosed in the patents generates an appropriate cogging torque serving as a load against a coil torque. In accordance with a combination of the cogging torque and coil torque, an ideal resultant torque is obtained.
Meanwhile, the coil torque and cogging torque exhibit a phase difference corresponding to about ¼ of the pole width therebetween. Accordingly, the cogging generating means is arranged at a position where the coil torque is zero during a rotation of the rotor.
In U.S. Pat. Nos. 4,620,139 and 4,757,222, as shown in
FIG. 10
, the cogging generating means comprises iron cores
440
coupled to or fitted to the stator yoke
420
in such a fashion that they are protruded from the stator yoke
420
toward the rotor magnet
310
. Alternatively, the cogging generating means may be provided by cutting out opposite arc-shaped peripheral portions of the stator yoke
420
, as shown in FIG.
11
. In this case, the cogging generating means comprises arc-shaped cutouts
450
. In both cases, however, there is a problem in that it is difficult to determine an accurate position of the cogging generating means because the position of the cogging generating means has an inseparable relation with the attachment position of the armature coil.
In both cases, an accurate position for installing the cogging generating means thereon is first determined with respect to each armature coil
430
attached to the stator coil
420
. The coupling or fitting of the iron core
440
to the stator coil
420
is carried out at the determined position. In the case wherein the arc-shaped cutouts are used as the cogging generating means, those cutouts are formed at positions determined as above, respectively. However, the position determination for the cogging generating means is very difficult unless a jig is used.
Since a pair of armature coils
430
are practically attached to the stator yoke
420
in such a fashion that they are opposite to each other, a great loss of magnetic force occurs at stator yoke portions where no armature coil is attached, thereby generating a reduced coil torque. As a result, an insufficient drive torque is obtained. This results in a considerable performance degradation.
On the other hand, in Japanese Patent Publication No. Heisei 7-213041, the cogging generating means comprises magnetic members
460
as shown in FIG.
12
. Each magnetic member
460
is positioned at an angle &thgr; (0<&thgr;<&pgr;, where &pgr; is an electrical angle and equal to 180°) from the dead point. In particular, the magnetic members have a screw construction so that they also serve as a fixing means for fixing the printed circuit board
410
and stator yoke
420
to each other.
In this case, however, the screw members preferentially have the function for fixing the printed circuit board
410
and stator yoke
420
to each other over the cogging generating function. For this reason, after the printed circuit board
410
and stator yoke
420
are fixed to each other, the screw members may have different gaps with respect to the associated rotor magnets
310
, respectively. As a result, the cogging torque generated by the cogging generating means may vary for different screw members.
In other words, a difference in fastening degrees of the screw members result in a variation in the magnetic force generated by the rotor magnets
310
, thereby generating an instable drive torque.
In the case of a miniature motor, furthermore, it is impossible to fasten the magnetic members
460
having a very small size unless a specific tool is used. Moreover, it
Ladas & Parry
Mullins Burton
Samsung Electro-Mechanics Co. Ltd.
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