Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-09-26
2003-09-02
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S208000
Reexamination Certificate
active
06614141
ABSTRACT:
This application is based on Application No. 2000-394725, filed in Japan on Dec. 26, 2000, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for manufacturing a stator having a stator core in which slots are formed at a ratio of two per phase per pole, and to an automotive alternator to which the stator is mounted.
2. Description of the Related Art
Generally, an automotive alternator includes: a stator constructed by installing a stator winding into 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 a 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 a tooth overlaps an adjacent pair of the magnetic poles relative to the radial direction.
FIG. 18
is a schematic diagram in which part of a stator such as that described in Japanese Patent Laid-Open No. HEI 4-26345, for example, is developed into a plan.
In
FIG. 18
, a stator core
60
is composed by forming a magnetic steel plate 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 slot
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 a group of the a-phase slots
61
a
, a b-phase winding phase portion
63
b
is constructed by winding conductor wires into a wave shape in a group of the b-phase slots
61
b
, and in addition, a c-phase winding phase portion
63
c
is constructed by winding conductor wires into a wave shape in a group of the c-phase slots
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 60° from each other.
A d-phase winding phase portion
63
d
is constructed by winding conductor wires into a wave shape in a group of the d-phase slots
61
d
, an e-phase winding phase portion
63
e
is constructed by winding conductor wires into a wave shape in a group of the e-phase slots
61
e
, and in addition, an f-phase winding portion
63
f
is constructed by winding conductor wires into a wave shape in a group of the f-phase slots
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 60° 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. Thus, 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.
Japanese Patent Laid-Open No. HEI 4-26345 described above does not disclose the construction of the stator winding
63
in detail, but if, for example, a stator winding is constructed using star-shaped winding units each composed by forming into a star shape an annular winding unit in which a conductor wire is wound for a predetermined number of winds, because the slots
61
are formed at a ratio of two per phase per pole, short-circuiting is more likely to occur between coil ends in coil end groups of the stator winding
63
. Thus, because the alternating-current outputs from the first and second alternating-current windings constituting the stator winding
63
are combined after being rectified by separate rectifiers, short-circuiting between the first and second alternating-current windings leads to poor power generation.
Because the star-shaped winding units are installed in the stator core so as to line up in six layers radially, when a cooling airflow generated by a cooling fan is allowed to flow through the coil end groups of the stator core from an inner circumferential side to an outer circumferential side, heat dissipation from the coil ends varies according to the radial position of the coil ends. Thus, depending on the arrangement of the coil ends in the winding phase portions constituting the first and second three-phase alternating-current windings, heat generated in either of the first and second three-phase alternating-current windings may not be effectively dissipated from the coil ends, making the temperature of the stator increase excessively, thereby leading to reduced output.
One countermeasure for solving such problems has been to construct the stator winding using short U-shaped conductor segments. In that case, because coil end groups of the stator winding can be constructed such that coil ends constituted by turn portions and joint portions of free end portions of the conductor segments are disposed so as to be separated circumferentially and radially, short-circuiting is less likely to occur between the coil ends and heat dissipation from the coil ends increases. However, because the slots are formed at a ratio of two per phase per pole, the number of conductor segments used increases significantly, complicating the process of inserting the conductor segments into the slots, and the number of joints betw
Adachi Katsumi
Asao Yoshihito
Oohashi Atsushi
Mitsubishi Denki & Kabushiki Kaisha
Nguyen Tran
LandOfFree
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