Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-10-09
2004-03-09
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S051000
Reexamination Certificate
active
06703759
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. 12
is a cross section of a conventional automotive alternator, and
FIG. 13
is a perspective of a rotor
107
in FIG.
12
.
This alternator is provided with: a case
3
constituted by a front bracket
1
and a rear bracket
2
made of aluminum; a shaft
6
disposed inside the case
3
, a pulley
4
being secured to a first end portion of the shaft
6
; a Lundell-type rotor
107
secured to the shaft
6
; fans
105
a
and
105
b
secured to first and second end surfaces of the rotor
107
; a stator
108
secured to an inner wall surface inside 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
; a brush holder
11
for accommodating the brushes
10
; a rectifier
12
electrically connected to the stator
108
for converting alternating current generated in the stator
108
into direct current; and a regulator
18
fitted onto the brush holder
11
, the regulator
18
adjusting the magnitude of the alternating voltage generated in the stator
108
.
The rotor
107
is provided with: a rotor coil
13
for generating magnetic flux on passage of an electric current; and a pole core
14
disposed so as to cover the rotor coil
13
, magnetic poles being formed in the pole core
14
by the magnetic flux from the rotor coil
13
. The pole core
14
is constituted by a first pole core portion
121
and a second pole core portion
122
which are alternately intermeshed with each other. The first pole core portion
121
and the second pole core portion
122
are made of iron, and are constituted by: first and second disk portions
201
and
202
which are surfaces perpendicular to an axis; first and second claw-shaped magnetic poles
123
and
124
having a tapered shape extending axially from the disk portions
201
and
202
so as to face each other; and a cylindrical portion
200
connecting the disk portions
201
and
202
to each other, a circumference of the cylindrical portion
200
being covered by the rotor coil
13
.
As shown in
FIGS. 14 and 15
, on side surfaces of the claw-shaped magnetic poles
123
and
124
each constituting a facing surface between adjacent first and second claw-shaped magnetic poles
123
and
124
, values of &agr; and values of &bgr; are equivalent, where &agr; is an angle formed between the side surface at a tip
123
A of a claw-shaped magnetic pole
123
or
124
and a radial line of the claw-shaped magnetic pole
123
or
124
, and &bgr; is an angle formed between the side surface at a root portion
123
B of a claw-shaped magnetic poles
123
or
124
and the radial line.
FIG. 16
is a perspective of the stator
108
in
FIG. 12
,
FIG. 17
is a perspective of a stator core
115
in
FIG. 12
, and
FIG. 18
is a partial plan of the stator core
115
in FIG.
17
.
The stator
108
is constituted by: a stator core
115
formed by laminating a plurality of steel sheets for passage of a rotating magnetic field from the rotor coil
13
; and a three-phase stator winding
116
through which an output current flows. The stator core
115
is constituted by: an annular core back
82
; and a plurality of teeth
81
extending radially inward from the core back
82
at a uniform pitch in a circumferential direction. The three-phase stator winding
116
is housed in a total of thirty-six slots
83
formed between adjacent teeth
81
. The teeth
81
are constituted by: tip portions
85
projecting in a circumferential direction of the stator
108
; and stanchion portions
86
connecting the tip portions
85
and the core back
82
. Gaps called opening portions
84
are formed between the tip portions
85
of adjacent teeth
81
.
Moreover, this example is a three-phase alternator in which the total number of slots
83
is thirty-six and the total number of claw-shaped magnetic poles
123
and
124
is twelve, the slots
83
being formed at a ratio of one per phase per pole.
In the automotive alternator of the above construction, an electric current is supplied from a battery (not shown) through the brushes
10
and the slip rings
9
to the rotor coil
13
, generating a 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 magnetic 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 magnetic 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 so as to have minimal 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 wires 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 preventing the magnetomotive force from increasing.
If attempts are made to increase the magnetomotive force by increasing the field current I while keeping the cross-sectional area s of the conductor wires 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 wires in the rotor coil
13
rises due to the increase in temperature, reducing the field current I and preventing the magnetomotive force from increasing after all.
On the other hand, as shown in
FIG. 19
, Japanese Patent Laid-Open No. HEI 11-164499 discloses an alternator aimed at increasing magnetomotive force by setting a ratio L1/L2 between an axial length L1 of the stator core
115
and an axial length L2 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
into 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 R1 of the claw-shaped magnetic poles
123
and
124
and an outside radius R2 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 automotive alternator according to the above Patent Laid-Open, no consideration at all has been given to the dimensions, shapes, etc., of the claw-shaped magnetic poles
123
and
124
, and for example, when the ratio between the radial thickness of the tips
123
A of the claw-shaped
Asao Yoshihito
Inoue Hirokazu
Oohashi Atsushi
Elkassabgi Heba Y.
Mitsubishi Denki & Kabushiki Kaisha
Sughrue & Mion, PLLC
Tamai Karl
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