Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-08-11
2002-04-16
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S261100, C310S045000, C310S062000, C310S179000
Reexamination Certificate
active
06373166
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an alternator driven by an internal combustion engine, for example, and relates to an automotive alternator mounted to an automotive vehicle such as a passenger car or a truck, for example.
2. Description of the Related Art
FIG. 20
is a cross section of a conventional automotive alternator, and
FIG. 21
is a perspective of a stator in FIG.
20
.
This alternator includes: a case
3
composed of an aluminum front bracket
1
and an aluminum rear bracket
2
; a shaft
6
disposed within the case
3
having a pulley
4
secured to a first end thereof; a Lundell-type rotor
107
secured to the shaft
6
; fans
105
a
and
105
b
secured to both axial end surfaces of the rotor
107
; a stator
108
secured to an inner wall within the case
3
; slip rings
9
secured to a second end of the shaft
6
for supplying electric current to the rotor
107
; a pair of brushes
10
sliding on surfaces of the slip rings
9
; brush holders
11
accommodating the brushes
10
; rectifiers
12
electrically connected to the stator
108
for converting alternating current generated in the stator
108
into direct current; and a regulator
18
fitted over the brush holder
11
for adjusting the magnitude of the alternating voltage generated in the stator
108
.
The rotor
107
includes a rotor coil
13
for generating magnetic flux on passage of electric current, and a pole core
14
disposed so as to cover the rotor coil
13
, magnetic poles being produced in the pole core
14
by the magnetic flux. The pole core
14
includes a first pole core portion
121
and a second pole core portion
122
which intermesh with each other. The first pole core portion
121
and the second pole core portion
122
are made of iron and include disk portions
201
and
202
which are perpendicular to an axial direction, tapered claw-shaped magnetic poles
123
and
124
extending axially from the disk portions
201
and
202
in opposite directions to each other, and a cylindrical portion
200
connecting the disk portions
201
and
202
to each other, the circumference of the cylindrical portion
200
being covered by the rotor coil
13
.
FIG. 22
is a perspective of the stator
108
in
FIG. 20
,
FIG. 23
is a perspective of a stator core
115
in
FIG. 22
, and
FIG. 24
is a partial plan of the stator core
115
.
The stator
108
includes a stator core
115
for passage of a rotating magnetic field from the rotor coil
13
, the stator core being formed by laminating a number of steel plates, and a stator winding
116
through which an output current flows. The stator core
115
includes an annular core back
82
, a number of teeth
81
extending radially inwards from the core back
82
at an even pitch in a circumferential direction. The stator winding
116
is housed in a total of thirty-six slots
83
formed between adjacent teeth
81
. The teeth include end portions
85
projecting in a circumferential direction of the stator
108
, and post portions
86
connecting the end portions
85
to the core back
82
. Spaces called opening portions
84
are formed between the end portions
85
of adjacent teeth
81
.
In the automotive alternator of the above construction, electric current is supplied from a battery (not shown) through the brushes
10
and the slip rings
9
to the rotor coil
13
, generating magnetic flux and giving rise to a magnetic field. At the same time, since the pulley
4
is driven by the engine and the rotor
107
is rotated by the shaft
6
, a rotating magnetic field is applied to the stator core
115
, generating electromotive force in the stator winding
116
and an output current is generated by an external load connected to the automotive alternator.
Now, the flux A generated by the rotor coil
13
leaves the first pole core portion
121
, which is magnetized with north-seeking (N) poles, crosses an air gap between the rotor
107
and the stator
108
, and enters the teeth
81
of the stator core
115
. This magnetic flux A then passes through the core back
82
, and flows from adjacent teeth across the air gap to the second pole core portion
122
, which is magnetized with south-seeking (S) poles.
The amount of flux, which determines the output of the alternator, is itself determined by the magnetomotive force of the rotating magnetic field from the rotor
107
and magnetic resistance of the above magnetic circuit followed by the magnetic flux A. Consequently, if the magnetomotive force is constant, then it is important to shape this magnetic circuit to have the least resistance.
Furthermore, in order to improve the magnetomotive force, it is necessary to increase AT (the field current I multiplied by the number of turns n of conductor in the rotor coil
13
), but AT is determined by installation space for the rotor coil
13
inside the pole core
114
. When the overall size of the rotor
107
is limited, it becomes necessary to reduce the cross-sectional area of the magnetic path through the pole core
114
in exchange for increases in installation space for the rotor coil
13
, and as a result the above-mentioned magnetic resistance increases, reducing the amount of magnetic flux passing through the pole core
114
, and the magnetomotive force does not increase.
If one attempts to increase the magnetomotive force by increasing the field current I while keeping the cross-sectional area s of the conductor and the number of turns n constant, the temperature of the rotor coil
13
increases due to copper loss in the rotor coil
13
, and the resistance of the conductor in the rotor coil
13
rises due to the increase in temperature, reducing the field current I, and the magnetomotive force does not increase after all.
On the other hand, as shown in
FIG. 25
, Japanese Patent Laid-Open No. HEI 11-164499 discloses an alternator aimed at increasing magnetomotive force by setting a ratio L
1
/L
2
between an axial length L
1
of the stator core
115
and an axial length L
2
of the cylindrical portion
200
within a range of 1.25 to 1.75, placing the disk portions
201
and
202
opposite the stator core
115
so that the magnetic flux A flows directly from the disk portions
201
and
202
to the stator core
115
, thereby increasing the cross-sectional area of the magnetic path through the pole core
114
, and setting a ratio between an outside radius R
1
of the claw-shaped magnetic poles
123
and
124
and an outside radius R
2
of the cylindrical portion
200
between 0.54 and 0.60, thereby increasing the cross-sectional area of the magnetic path through the cylindrical portion
200
.
However, in the case of this alternator, the figures are set with the aim of improving the output of the alternator per unit weight, and one problem has been that output decreases at low-speed rotation due to magnetic saturation.
Furthermore, by increasing the area of the disk portions
201
and
202
facing the stator core
115
, thereby increasing the amount of overlap, the cross-sectional area of passages through valley portions
410
between the claw-shaped magnetic poles
123
and
124
, which are passages for cooling ventilation, is reduced, increasing resistance to ventilation flow inside the rotor
107
, and another problem has been that when a large field current I flows through the rotor coil
13
, the cooling of the rotor coil
13
has been insufficient, increasing the resistance of the conductors in the rotor coil
13
and reducing the field current I, thereby preventing output from being increased.
SUMMARY OF THE INVENTION
The present invention aims to solve the above problems and an object of the present invention is to provide an alternator enabling the magnetic flux to be increased by increasing the cross-sectional area of the magnetic path, and also enabling output to be improved by reducing copper loss in the rotor coil.
To this end, according to the present invention, there is provided an alternator being such that a ratio (L
2
/L
1
) between an axial length L
1
of disk portions and a length L
2
Adachi Katsumi
Asao Yoshihito
Mitsubishi Denki & Kabushiki Kaisha
Mullins Burton S.
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