Direct current motor using magnets with extensions

Details Direct current motor using magnets with extensions Direct current motor using magnets with extensions

2000-03-28

2002-01-29

Nguyen, Tran (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S154230, C310S049540

Reexamination Certificate

active

06342744

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATION
The present application relates to and incorporates herein by reference Japanese Patent Applications No. 11-142042 filed on May 21, 1999, No. 11-203769 filed on Jul. 16, 1999 and No. 11-270566 filed on Sep. 24, 1999.
BACKGROUND OF THE INVENTION
The present invention relates to direct current motors having permanent magnets.
A conventional direct current (d.c.) motor
20
is comprised of permanent magnets
21
and
22
, an armature
23
, a commutator
24
, brushes
25
and the like as shown in
FIGS. 13A
to
13
C. In this motor, the armature
23
rotates as shown in the order of
FIGS. 13A
,
13
B and
13
C, when direct current power is supplied thereto.
Specifically, the armature
23
has an armature core
26
and armature coils
27
. A plurality of teeth
26
a
is formed on the core
26
. Each coil
27
is wound around five teeth
26
a,
although only one is shown in the figures. The coils
27
are wound in a distributed winding form.
The commutator
24
has a plurality of segments
24
a
on which the brushes
25
slide, so that the direct current flows from the brushes
25
to the coils
27
through the segments
24
a
of a commutator
24
. Thus, the armature
23
rotates in the clockwise direction (arrow X) in the figures, as the direction of current flowing in the coils
27
is reversed.
The current supplied to the coil
27
from the brush
25
is changed as shown in
FIGS. 14A
to
14
C. It is assumed that the current I flows from right to left as shown in
FIG. 14A
, and that the commutator
24
moves to the right as shown in
FIG. 14B
relative to the brush
15
as the armature
23
rotates. The brush
25
bridges two adjacent segments
24
a
to supply the coil
27
with shorting current i. The current I flows from the left to the right in the coil
27
as shown in
FIG. 14C
, as the armature
23
rotates further. That is, the direction of the current I flowing in the coil
27
is reversed, when the armature
23
rotates as shown in the order of
FIGS. 14A
,
14
B and
14
C. In this instance, the current which changes by
2
I from +I to −I is supplied from the brush
25
.
FIGS. 14A
to
14
C correspond to
FIGS. 13A
to
13
C. When the armature
23
rotates as shown in the order of
FIGS. 13A
,
13
B and
13
C, the direction of current I in the coil is reversed. The direction of the magnetic field in the core
26
wound with the core coil
27
is reversed. The rotating force is generated to rotate the armature
23
by the electromagnetic force of the coils
27
and the magnetic force of the magnets
21
and
22
.
The reversion of current flowing in the coil
27
during the period of shorting by the brush
25
is defined as commutation. This relation is expressed in the following commutation equation.
L
(
di/dt
)+
e+Rci+R
2(
I+i
)−
R
1(
I−i
)=0
In the above equation, L(di/dt) is a reactance voltage generated by an inductance of the coil
27
shorted by the brush
25
, and e is an induction voltage generated in the coil
27
when the armature
23
rotates. Rc is a resistance of the coil
27
shorted by the brush
25
. R
1
and R
2
are contact resistances between the brush
25
and the commutator
24
. I is a current supplied form the brush
25
, and i is a shorting current of the coil
27
shorted by the brush
25
.
The shorting current i changes linearly as shown by the dotted line in
FIG. 15
, as long as the reactance voltage L(di/dt) of the coil
27
and the induction voltage e is negligible during the commutation period. In this instance, the commutation is effected linearly and most favorable.
However, the reactance voltage and the induction voltage are generated in the coil
27
in fact. The shorting current i therefore flows with a delay in time relative to the linear commutation characteristics as shown by the solid line in
FIG. 15
, resulting in an insufficient commutation. This insufficient commutation causes spark discharges at the rear end of the brush
25
, when the commutation terminates. The spark discharges causes noise and brush wear.
It is proposed to counter this problem, that is, improve the commutation operation by moving the brush in the counter-clockwise direction in FIG.
13
. The brush is moved to reduce the influence of the induction voltage e. Specifically, the induction voltage e is generated as a counter-electromotive force in the coil
27
by changes in the magnetic flux amount &PHgr; passing through the coil
27
. This voltage e is expressed as follows.
e=−d&PHgr;/dt
That is, the induction voltage e is generated in proportion to the speed of reduction in the magnetic flux amount &PHgr; passing through the coil
27
.
The induction voltage e is shown in FIG.
16
. Specifically,
FIG. 16
shows changes in the magnetic flux amount &PHgr; passing through the coil
27
and hence passing through the core
26
(five teeth
26
a
) around which the coil
27
is wound, and the induction voltage e generated in the coil
27
in response to the change in the magnetic flux amount &PHgr;. In
FIG. 16
, the magnetic flux amount &PHgr; and the induction voltage e are shown with respect to a reference position (0°) which corresponds to FIG.
13
B. That is, the reference position is defined as the position where the center of the core
26
(five teeth
26
a
) wound with the coil
27
coincides with the center of the magnet
21
or
22
.
When no current flows in the coil
27
, only the magnetic flux of the permanent magnets
21
and
22
passes through the coil
27
. In this instance, the magnetic flux amount &PHgr; is maximal when the rotation position of the armature
23
is at the reference position (
FIG. 13B
) as shown by (A) in FIG.
16
.
When the current flows in the coil
27
, however, it generates the magnetic force which influence the magnetic flux of the magnets
21
and
22
. As a result, the magnetic flux amount &PHgr; of the coil
27
changes with the rotation position of the armature
23
as shown by (B) in
FIG. 16
, because the current is reversed during the commutation period, that is, when the armature
23
rotates as shown in the order of
FIGS. 13A
,
13
B and
13
C. That is, the magnetic flux amount &PHgr; changes from positive to negative, when the armature
23
passes through the reference position. As a result, the magnetic flux amount &PHgr; which actually passes through the coil
27
changes as shown by (C) in FIG.
16
. This amount is a sum of the flux amounts indicated by (A) and (B). Thus, the actual magnetic flux amount &PHgr; becomes maximum before the armature
23
rotates to the reference position. As a result, the induction voltage e of the coil
27
changes from negative to positive when the total magnetic flux amount becomes the maximum. For this reason, the induction voltage e is generated in a manner to delay the commutation and delay the reversion of the shorting current i, causing the insufficient commutation.
Therefore, the influence of the induction voltage e in the coil
27
is minimized by moving the position of the brush
25
in the direction opposite the rotation of the armature
23
, that is, in the counter-clockwise direction in FIG.
13
. In practice, the position of the brush
25
is determined based on not only the induction voltage but also the reactance voltage.
It is however difficult to maintain good commutation operation, because the current flowing in the coil
27
and the rotation speed of the motor change from time to time. For instance, in the case of a blower motor used for an automotive air conditioner unit, the position where the total magnetic flux amount &PHgr; attains the maximum moves to a position (negative side in
FIG. 16
) opposite the rotation direction at high load and high rotation speed conditions because more current is supplied. The induction voltage e caused by the total magnetic flux amount &PHgr; also increases as the rotation speed increases. Further, the reactance voltage also increases as the current in the coil
27
increases. Thus, the brush need be moved more for good com

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