Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-10-31
2002-08-13
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S254100, C310S180000, C310S184000
Reexamination Certificate
active
06433456
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an alternator driven by, for example, an internal combustion engine and, more particularly, to a structure of a stator of an automotive alternator mounted on a passenger car, a truck, etc.
2. Description of the Related Art
FIG. 8
is a sectional side elevation of a conventional automotive alternator,
FIG. 9
is a perspective view of a rotor of
FIG. 8
,
FIG. 10
is a front view of a stator core applied to a stator of the conventional automotive alternator, and
FIG. 11
is a circuit diagram of the conventional automotive alternator. The conventional alternator shown in the drawings includes: a case
3
composed of an aluminum front bracket
1
and an aluminum rear bracket
2
; a shaft
5
rotatably disposed in the case
3
and which has a pulley
4
secured to one end thereof; a Lundell-type rotor
6
secured to the shaft
5
; fans
7
secured to both ends of the rotor
6
; a stator
8
secured to an inner wall surface of the case
3
; a slip ring
9
secured to the other end of the shaft
5
and which supplies electric current to the rotor
6
; a brush
10
that slides in contact with the slip ring
9
; a brush holder
11
accommodating the brush
10
; a rectifier
12
electrically connected to the stator
8
to convert alternating current generated in the stator
8
into direct current; a heat sink
13
fitted on the brush holder
11
; and a regulator
14
adhesively fastened to the heat sink
13
and which adjusts a magnitude of an alternating voltage generated in the stator
8
.
The rotor
6
is equipped with a rotor coil
15
for generating magnetic fluxes by passing an electric current, and a pole core
16
covering the rotor coil
15
in which magnetic poles are produced by the magnetic fluxes. The pole core
16
has a pair of a first pole core assembly
17
and a second pole core assembly
18
that intermesh with each other. The first pole core assembly
17
and the second pole core assembly
18
are made of iron and have claw-shaped magnetic poles
19
and
20
at their ends. Spaces are formed between adjacent claw-shaped magnetic poles
19
and
20
to prevent magnetic fluxes from leaking from between the claw-shaped magnetic poles
19
and
20
, and also to function as cooling passages for cooling the rotor coil
15
.
The stator
8
is provided with a stator core
22
and two sets of three-phase stator coils
23
in which conductors are wound around the stator core
22
with a phase difference of a 30-degree electrical angle (see FIG.
10
and FIG.
11
). The stator core
22
is formed by punching a steel sheet into a comb-like plate with equidistantly arranged teeth, and by rolling or laminating the comb-like plate into an annular shape. An inner periphery of the stator core
22
has slots
25
and teeth
24
that extend in the axial direction.
This example includes the two sets of the three-phase stator coils
23
, and the rotor
6
has twelve magnetic poles, two three-phase portions corresponding to each pole. Seventy-two slots
25
and teeth
24
, respectively, are formed. The annular stator core
22
has the slots
25
formed at equal intervals of 5-degree mechanical angles (360°/72). At this time, the seventy-two slots uniformly correspond to the a twelve poles, so that the slots
25
are formed at uniform intervals of 30-degree electrical angles. The two sets of three-phase stator coils
23
in Y-Y connection are respectively provided with a phase difference of a 30-degree electrical angle in the slots
25
and electrically connected to rectifiers
12
.
In an automotive alternator having the above construction, current is supplied by a battery (not shown) through the brush
10
and a slip ring
9
to the rotor coil
15
so as to generate magnetic fluxes, whereby claw-shaped magnetic poles
19
of the first pole core assembly
17
are polarized with north-seeking (N) poles, while the claw-shaped magnetic poles
20
of the second pole core assembly
18
are polarized with south-seeking (S) poles.
The pulley
4
is rotated by an engine, and the rotor
6
rotates together with the shaft
5
. This causes a rotating magnetic field to be imparted to the stator coil
23
, and an electromotive force is generated. The AC electromotive force is converted into direct current by means of the rectifiers
12
, and a magnitude of the direct current is adjusted by the regulator
14
before recharging the battery.
In the automotive alternator, one each of slots
25
of the stator core
22
is provided for each set and each phase of the stator coils
23
and for each magnetic pole of the rotor
6
. Since there are seventy-two slots
25
and teeth
24
, the circumferential widths of the teeth
24
are small; hence, there are fewer chances in which leakage magnetic fluxes produced between adjoining claw-shaped magnetic poles
19
and
20
of the rotor
6
leak out through the same teeth
24
.
FIG. 12
illustrates a positional relationship between the teeth
24
, the slots
25
, and the claw-shaped magnetic poles
19
and
20
.
FIG. 12A
shows a state wherein the teeth
24
overlap with only the claw-shaped magnetic pole
19
,
FIG. 12B
shows a state wherein the teeth
24
overlap with the claw-shaped magnetic poles
19
and
20
, and
FIG. 12C
shows a state wherein the teeth
24
overlap with only the claw-shaped magnetic pole
20
. Thus, in the conventional automotive alternator, the teeth
24
have a narrow circumferential width, and the time during which magnetic fluxes leak to the teeth
24
is short. This means a less reduction in effective magnetic fluxes for the stator coils
23
caused by leakage magnetic fluxes, leading to reduced pulsation in magnetic fluxes. An art similar to that of the automotive alternator described above has been disclosed in Japanese Unexamined Patent Application Publication No. 4-26345.
In the conventional automotive alternator having the construction set forth above, if slot openings are arranged at equal intervals of 30-degree electrical angles, then spatial fifth and seventh higher harmonics of magnetic flux density waveforms do not appear. This is illustrated in
FIG. 13
prepared by the inventors of the application concerned who have performed analyses of electromagnetic fields. Referring to
FIG. 13
, the axis of abscissa indicates the interval of slot openings. Electrical angles are at equal intervals at 30 degrees, while they are at nonuniform intervals at, for example, 24 degrees (24 degrees and 36 degrees are repeated). The axis of ordinates indicates a ratio of stator magnetomotive force higher harmonics to a fundamental wave. However, the magnetomotive force higher harmonics of the stator
8
have large spatial eleventh and thirteenth higher harmonics. Hence, if the magnetomotive force higher harmonics of the rotor
6
include the eleventh or thirteenth higher harmonics, then their mutual interference prevents adequate suppression of magnetic flux pulsation, so that fluctuation in a generated voltage cannot be adequately controlled. Thus, there has been a problem in that a magnetic attraction force is produced between the claw-shaped magnetic poles
19
and
20
of the rotor
6
and the stator
8
, and resonance takes place in the stator
8
, the case
3
, etc. or the claw-shaped magnetic poles
19
and
20
of the rotor
6
vibrate, generating noises uncomfortable to an occupant.
Furthermore, if slots are disposed at equal pitches, Ad then marked synchronous pulsation based on the number of slots takes place, producing noises that are even more uncomfortable.
When the gap between adjoining claw-shaped magnetic poles
19
and
20
can be reduced, if the teeth
24
are made narrower accordingly, then a problem arises in that a main magnetic flux decreases although invalid magnetic fluxes can be reduced.
SUMMARY OF THE INVENTION
The present invention has been made with a view toward solving the problems described above, and it is an object of the present invention to provide an automotive alternator capable of reducing invalid magnetic fluxes an
Adachi Katsumi
Asao Yoshihito
Higashino Kyoko
Mullins Burton S.
Sughrue & Mion, PLLC
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