Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-02-12
2002-10-29
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S254100
Reexamination Certificate
active
06472793
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based on Application No.2000-242491, filed in Japan on Aug. 10, 2000, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an alternator for use in a vehicle in which a voltage develops in a stator in accordance with rotation of a rotor.
2. Description of the Related Art
FIG. 13
is a cross-sectional view showing a conventional alternator for a vehicle,
FIG. 14
is a perspective view showing a rotor for use in the conventional alternator for the vehicle,
FIG. 15
is a perspective view showing a stator for use in the conventional alternator,
FIG. 16
is a perspective view showing an iron core of the stator as shown in
FIG. 15
,
FIG. 17
is a plan view showing the essential part of the stator iron core, and
FIG. 18
is an illustration of a circuit of the conventional alternator for the vehicle.
In
FIG. 13
, the conventional alternator for the vehicle is made up of a case
3
comprising front and rear brackets
1
and
2
made of aluminum, a shaft
6
provided in the interior of the case
3
and having one end portion fixedly mounted to a pulley
4
, a Lundell Type rotor
7
fixedly fitted over the shaft
6
, fans
5
fixedly mounted to both end portions of the rotor
7
in its axial directions, a stator
8
fixedly secured to the case
3
to surround the rotor
7
, slip rings
9
fixedly mounted to the other end portion of the shaft
6
for current supply to the rotor
7
, a pair of brushes
10
made to slide on a surface of the slip rings
9
, a brush holder
11
accommodating the brushes
10
, a rectifier
12
for rectifying an alternating current induced in the stator
8
into a direct current, and a regulator
18
fitted in the brush holder
11
for regulating the magnitude of an AC voltage developed in the stator
8
.
As
FIG. 14
shows, the rotor
7
is composed of a field coil
13
for generating magnetic flux on passage of electric current, and first and second pole core members
21
and
22
placed to cover the field coil
13
, magnetic poles being formed in the pole core members
21
and
22
by the magnetic flux generated in the field coil
13
. In addition, the first and second pole core members
21
and
22
, being made of iron, are constructed such that claw-like (tooth-like) magnetic poles
23
and
24
whose outermost-diameter surfaces (surfaces having the largest diameter) have a generally trapezoidal configuration are protrusively formed at an equiangular pitch (at an equal interval) in circumferential directions on its outer circumferential edge section, with the first and second pole core members
21
and
22
being fixedly fitted over the shaft
6
to be in opposed relation to each other so that these claw-like magnetic poles
23
and
24
engage with each other.
Furthermore, as
FIG. 15
shows, the stator
8
is composed of a cylindrical stator iron core
15
made by putting magnetic steel plates on top of each other and a stator winding
16
wound around the stator iron core
15
. The stator iron core
15
is, as shown in
FIGS. 16 and 17
, made up of a ring-like core back
150
and a plurality of teeth
151
made to extend radially inwardly from the core back
150
so that they are arranged at an equiangular pitch in circumferential directions. In addition, the stator winding
16
is accommodated in each of slots
152
defined between the adjacent teeth
151
. Still additionally, each of the teeth
151
comprises a tip portion
151
a
having a larger thickness (width) along the circumferential direction of the stator iron core
15
and a base (column) portion
151
b
making a connection between the tip portion
151
a
and the core back
150
, with a slot opening portion
153
being defined between the adjacent tip portions
151
a.
In this connection, to define a uniform air gap &dgr; between the rotor
7
and the stator
8
, the tip portion
151
a
of each of the teeth
151
is formed so that its inner circumferential surface has a concave configuration, while the claw-like magnetic poles
23
and
24
are made so that their outermost-diameter surfaces have a convex configuration.
In this conventional alternator for the vehicle, as shown in
FIG. 18
, the stator winding
16
is constructed as one three-phase alternating current winding in a manner that three winding phase groups
161
are coupled in the form of three-phase Y-connection. The rectifier
12
comprises diodes
120
and
121
.
In this construction, the number of magnetic poles in the rotor
7
is twelve in number, and the slots
15
are formed at 36 places in the stator iron core
15
to accommodate the stator winding
16
constructed as one three-phase alternating current winding. This means that the number of slots is one per pole per phase.
In the conventional alternator for vehicles thus constructed, a current is supplied from a battery (not shown) through the brushes
10
and the slip rings
9
to the field coil
13
, thereby generating a magnetic flux. Owing to this magnetic flux, the claw-like magnetic poles
23
of the first pole core member
21
are magnetized with north-seeking (N) poles, while the claw-like magnetic poles
24
of the second pole core member
22
are magnetized with south-seeking (S) poles. In addition, a flow of the magnetic flux takes place as indicated by an arrow A in FIG.
13
. That is, the magnetic flux advances from the claw-like magnetic pole
23
through the opposed tooth
151
to the stator iron core
15
, and further flows through the core back
150
, the tooth
151
and the claw-like magnetic pole
24
facing the same tooth
151
to enter the second pole core member
22
, and still further passes through the proximal portion of the second pole core member
22
to reach the first pole core
21
.
Meanwhile, the pulley
4
is driven by an engine to rotate the rotor
7
through the shaft
6
. The rotation of the rotor
7
causes a rotating magnetic field to be given to the stator iron core
15
so that an electromotive force is induced in the stator winding
16
. The alternating current electromotive force produced in the stator
8
is rectified into a direct current by the rectifier
12
, and the output voltage thereof is adjusted in magnitude through the use of the regulator
18
, thereby accomplishing charging of the battery.
However, the conventional alternator for vehicles thus constructed will create the following problems. In a case in which the dimension of the slot opening portion
153
in its circumferential directions is made smaller in order to reduce the magnetic resistance of the air gap &dgr; between the stator
8
and the rotor
7
, when the central position in the circumferential direction between the adjacent claw-like magnetic poles
23
and
24
is aligned with the circumferential-direction central position of the inner circumferential surface of the tip portion
151
a
of the tooth
151
in the case of being viewed from a radial direction, a portion of each of the claw-like magnetic poles
23
and
24
overlaps concurrently with the tip portion
151
a
of the tooth
151
. This reduces the magnetic flux variation to lessen magnetic noise. On the other hand, as indicated by an arrow B in
FIG. 19
, the magnetic flux fails to flow from the claw-like magnetic pole
23
through the tooth
151
to the core back
150
, but flowing from the outermost-diameter surface and shoulder portion of the claw-like magnetic pole
23
through the tooth
151
to the claw-like magnetic pole
24
, that is, the ineffective magnetic flux quantity increases; therefore, the bypassing quantity of the magnetic flux generated in the field coil
13
toward the stator winding
16
decreases accordingly to result in a decrease in output at low-speed rotation regions.
Furthermore, if the output at the low-speed rotation regions is increased by eliminating the overlapping between the claw-like magnetic poles
23
,
24
and the tooth
151
in a case in which the central position in the circumferential direction bet
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