Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-11-27
2004-03-30
Mullins, Burton (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S179000, C310S180000, C310S184000
Reexamination Certificate
active
06713928
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an automotive alternator mounted with a stator having a stator core in which slots are formed at a ratio of two per phase per pole.
2. Description of the Related Art
Generally, an automotive alternator includes: a stator composed of a stator winding installed in a cylindrical stator core in which slots extending axially are formed at an even angular pitch in a circumferential direction; and a rotor having a field winding disposed on an inner circumferential side of the stator. The slots are disposed in the stator core at a ratio of one per phase per pole, in proportion to the number of phases in the stator winding and the number of magnetic poles in the rotor.
When the slots are disposed at a ratio of one per phase per pole in this manner, the amount of time that any given tooth formed between the slots overlaps an adjacent pair of the magnetic poles relative to a radial direction is long, leading to increased magnetic flux leakage. This magnetic flux leakage reduces effective magnetic flux and gives rise to surges in the magnetic flux, resulting in fluctuations in the generated voltage and disturbing the output waveform, which causes ripples when the alternating current is converted into direct current.
Thus, an attempt has been proposed in Japanese Patent Laid-Open No. HEI 4-26345, for example, to reduce magnetic flux leakage by disposing the slots at a ratio of two per phase per pole to shorten the amount of time that any given tooth overlaps an adjacent pair of the magnetic poles.
FIG. 9
is a schematic diagram in which part of a first stator such as that described in Japanese Patent Laid-Open No. HEI 4-26345, for example, is developed into a plan.
In
FIG. 9
, a stator core
60
is composed of a magnetic steel plate formed into a cylindrical shape, slots
61
extending axially being disposed therein at an even angular pitch in a circumferential direction at a ratio of two per phase per pole. Here, for twelve magnetic poles in a rotor (not shown), seventy-two slots
61
are disposed in the stator core
60
so as to obtain a stator winding
63
composed of first and second three-phase alternating-current windings. The seventy-two slots
61
are disposed at a pitch corresponding to an electrical angle of 30° from each other, being arranged in order of an a-phase slot
61
a
, a d-phase slot
61
d
, a b-phase slot
61
b
, an e-phase slot
61
e
, a c-phase slot
61
c
, and an f-phase slots
61
f
repeatedly in a circumferential direction.
An a-phase winding phase portion
63
a
is constructed by winding conductor wires into a wave shape in the a-phase slot group
61
a
, a b-phase winding phase portion
63
b
is constructed by winding conductor wires into a wave shape in the b-phase slot group
61
b
, and a c-phase winding phase portion
63
c
is constructed by winding conductor wires into a wave shape in the c-phase slot group
61
c
. The first three-phase alternating-current winding is constructed by forming the a-phase, b-phase, and c-phase winding phase portions
63
a
,
63
b
, and
63
c
wound in this manner into a Y-connection (an alternating-current connection). Here, the a-phase, b-phase, and c-phase slots
61
a
,
61
b
, and
61
c
into which the a-phase, b-phase, and c-phase winding phase portions
63
a
,
63
b
, and
63
c
are inserted have a phase difference corresponding to an electrical angle of 120° from each other.
A d-phase winding phase portion
63
d
is constructed by winding conductor wires into a wave shape in the d-phase slot group
61
d
, an e-phase winding phase portion
63
e
is constructed by winding conductor wires into a wave shape in the e-phase slot group
61
e
, and an f-phase winding phase portion
63
f
is constructed by winding conductor wires into a wave shape in the f-phase slot group
61
f
. The second three-phase alternating-current winding is constructed by forming the d-phase, e-phase, and f-phase winding phase portions
63
d
,
63
e
, and
63
f
wound in this manner into a Y-connection. Here, the d-phase, e-phase, and f-phase winding phase portions
63
d
,
63
e
, and
63
f
have a phase difference corresponding to an electrical angle of 120° from each other. Furthermore. the d-phase, e-phase, and f-phase winding phase portions
63
d
,
63
e
, and
63
f
have a phase difference corresponding to an electrical angle of 30° from the a-phase, b-phase, and c-phase winding phase portions
63
a
,
63
b
, and
63
c
, respectively.
A stator is prepared by installing these six winding phase portions
63
a
,
63
b
,
63
c
,
63
d
,
63
e
, and
63
f
in the stator core
60
. In an automotive alternator constructed in this manner, alternating-current outputs from the first and second three-phase alternating-current windings are each rectified by separate rectifiers, and then the rectified outputs are combined.
Thus, because the slots
61
are disposed at a ratio of two per phase per pole, portions of a tooth
62
overlapping an adjacent pair of the magnetic poles relative to the radial direction are dramatically reduced. Hence, magnetic flux leakage is reduced, enabling reductions in effective magnetic flux to be suppressed. Similarly, the generation of surges in the magnetic flux is suppressed, reducing fluctuations in the generated voltage and disturbances to the output waveform, thereby reducing ripples when the alternating current is converted into direct current.
In automotive alternators of the above construction, because the slots
61
of the stator are formed at a ratio of two per phase per pole, the number of slots
61
is greater than when the slots are formed at a ratio of one per phase per pole, giving rise to the following problems:
a) As shown in
FIG. 10
, a circumferential dimension (L) of the slots
61
is small, becoming 2d>L in relation to a radial dimension (d) of conductor wires
64
, resulting in the conductor wires
64
being housed in the slots
61
at random, thereby making the space factor of the conductor wires
64
in the slots
61
low and the ratio occupied by a space portion high, and since there are also few contacting portions between the teeth
62
and the conductor wires
64
or contacting portions among the conductor wires
64
, heat transfer from the conductor wires
64
to the stator core
60
or from one conductor wire
64
to another is low, making temperature increases in the stator winding
63
high, thereby leading to declines in output and declines in heat durability;
b) Because width dimensions of the teeth
62
are reduced, reducing the rigidity of the teeth
62
, electromagnetic noise generated by the teeth
62
due to circumferential vibrations is increased;
c) Because circumferential dimensions of the opening portions
65
of the slots
61
are small, the frequency with which the conductor wires
64
come into contact with flange portions
67
of tip portions of the teeth
62
when the conductor wires
64
are installed from radially inside toward the outside increases, making electrical insulation of the conductor wires
64
, which are coated with an electrical insulator, poor; and
d) Because gaps arise easily between wedges
66
and the conductor wires
64
on the radially innermost side, and because circumferential projection portions on the flange portions
67
for hooking the wedges
66
are small, there is a risk that the wedges
66
will oscillate and dislodge from the opening portions
65
.
SUMMARY OF THE INVENTION
The present invention aims to solve the above problems and an object of the present invention is to provide an automotive alternator capable of reducing the magnitude of temperature increases and electromagnetic noise in a stator.
In order to achieve the above object, according to one aspect of the present invention, there is provided an automotive alternator including:
a rotor fixed to a shaft rotatably supported in a case; and
a stator provided with:
a cylindrical stator core supported in the case so as to envelop the rotor, slots extending axially being formed in the stator core so as to lin
Asao Yoshihito
Oohashi Atsushi
Takizawa Takushi
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