U.S. patent application number 09/738318 was filed with the patent office on 2001-10-18 for automotive alternator.
Invention is credited to Asao, Yoshihito, Higashino, Kyoko.
Application Number | 20010030487 09/738318 |
Document ID | / |
Family ID | 18625456 |
Filed Date | 2001-10-18 |
United States Patent
Application |
20010030487 |
Kind Code |
A1 |
Higashino, Kyoko ; et
al. |
October 18, 2001 |
Automotive alternator
Abstract
In an automotive alternator having a case in which air intake
vents 1a and air discharge vents 1b are disposed, a rotor, which is
fastened to a shaft such that claw-shaped magnetic poles intermesh,
has as a pair of fans having a plurality of blades and fastened to
the axial end surfaces of poles cores, and is rotatably disposed in
the case, a stator core to which a plurality of slots are formed
and a stator having a stator winding to be accommodated in the
slots, the slots are formed in an even number, each of the
claw-shaped magnetic poles is formed in an even number, and said
blades of the pair of fans are formed in the same odd number,
respectively. With this construction, there can be provided a small
automotive alternator which has a high output and an excellent cost
performance and in which fans generate a low level of noise.
Inventors: |
Higashino, Kyoko; (Tokyo,
JP) ; Asao, Yoshihito; (Tokyo, JP) |
Correspondence
Address: |
SUGHRUE, MION, ZINN, MACPEAK & SEAS
2100 Pennsylvania Avenue, N.W.
Washington
DC
20037
US
|
Family ID: |
18625456 |
Appl. No.: |
09/738318 |
Filed: |
December 18, 2000 |
Current U.S.
Class: |
310/263 ;
310/60R; 310/61; 310/62 |
Current CPC
Class: |
H02K 19/16 20130101;
H02K 1/16 20130101; H02K 9/06 20130101; H02K 1/243 20130101 |
Class at
Publication: |
310/263 ; 310/62;
310/60.00R; 310/61 |
International
Class: |
H02K 001/22; H02K
009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 14, 2000 |
JP |
2000-113507 |
Claims
What is claimed is:
1. An automotive alternator including, a case having a plurality of
air intake vents disposed in the axial surface thereof and a
plurality of air discharge vents disposed in the radial surface
thereof, a rotor having a pair of pole cores including claw-shaped
magnetic poles projecting radially externally from the outer
circumferential perimeters thereof at even pitch, respectively,
fastened to a shaft such that said claw-shaped magnetic poles
intermesh and rotatably disposed in said case, said pair of pole
cores having a pair of fans, which include a plurality of blades
around the outer circumferences thereof, and being fastened to the
axial end surfaces thereof; and a stator fastened to said case so
as to cover the outer circumference of said rotor, and having a
stator core including a plurality of slots formed around the inner
circumference thereof facing said rotor and a stator winding
accommodated in said slots, wherein: said slots are formed in an
even number, each of said claw-shaped magnetic poles is formed in
an even number, and said blades of said pair of fans are formed in
the same odd number, respectively.
2. An automotive alternator according to claim 1, wherein the
number of said fan blades is less than one-half the total number of
said pair of claw-shaped magnetic poles.
3. An automotive alternator according to claim 1, wherein parts to
be cooled are housed in said case at a rear-end and the amount of
wind generated by a fan at a front-end is larger than the amount of
wind generated by a fan at said rear-end.
4. An automotive alternator according to claim 3, wherein the
outlet angle of said fan at said front-end is larger than the
outlet angle of said fan at said rear-end.
5. An automotive alternator according to claim 3, wherein the
outside diameter of said front-end fan is larger than the outside
diameter of said rear-end fan.
6. An automotive alternator according to claim 1, wherein said
stator winding includes a plurality of windings in each of which
one strand of wire is bent back outside said slots at the end
surfaces of said stator core and wound into wave winding so as to
alternately occupy an inner layer and an outer layer in a slot
depth direction within said slots a predetermined number of slots
apart, and said strand of wire bent back outside said slots at the
end surfaces of said stator core is arranged in a circumferential
direction, thereby constituting coil end groups having
approximately the same shape.
7. An automotive alternator according to claim 1, wherein said
stator winding includes a plurality of windings in each of which
one long strand of wire is bent back outside said slots at the end
surfaces of said stator core and wound into the wave winding so as
to alternately occupy an inner layer and an outer layer in a slot
depth direction within said slots a predetermined number of slots
apart, and the turned portions of said strand of wire bent back
outside said slots at the end surfaces of said stator core are
arranged in a circumferential direction, thereby constituting coil
end groups, said coil ends having approximately the same shape at
said front-end and at said rear-end.
8. An automotive alternator according to claim 1, wherein the
number of said slots is set to two in each pole and in each phase.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a vehicle-mounted
automotive alternator, and more particularly, to the number of
blades of fans mounted on a rotor.
[0003] 2. Description of the Related Art
[0004] FIG. 24 is a sectional view showing a construction of an
ordinary automotive alternator. FIG. 25 is a perspective view of a
rotor shown in FIG. 24.
[0005] The automotive alternator is arranged such that a
Lundell-type rotor 7 is rotatably mounted in a case 3 composed of
an aluminum front bracket 1 and an aluminum rear bracket 2 through
a shaft 6, and a stator 8 is fastened to the inner wall surface of
the case 3 so as to cover the inner circumference of the rotor
7.
[0006] The shaft 6 is rotatably supported by the front bracket 1
and the rear bracket 2. A pulley 4 is fastened to an end of the
shaft 6 so as to transmit the rotational torque of an engine to the
shaft 6 through a belt (not shown).
[0007] Slip rings 9 are fastened to the other end of the shaft 6 to
supply current to the rotor 7 and a pair of brushes 10 are
accommodated in a brush holder 11 disposed in the case 3 so as to
be in sliding contact with the slip rings 9. A regulator 18 is
adhered to a heat sink 17 fitted to the brush holder 11 to regulate
the magnitude of AC voltage generated by the stator 8. Rectifiers
12, which are electrically connected to the stator 8, are mounted
in the case 3 to rectify alternate current generated by the stator
8 to direct current.
[0008] The rotor 7 includes a rotor coil 13 for generating magnetic
flux on passage of electric current and a pair of pole cores 20 and
21 disposed so as to cover the rotor coil 13, magnetic poles being
formed in the pole cores 20 and 21 by magnetic flux generated in
the rotor coil 13. The pair of poles cores 20 and 21 are made of
iron and have cylindrical core base portions 22a and 23a and a
plurality of claw-shaped magnetic poles 22 and 23 disposed radially
externally on the outer circumferential perimeters of the core base
portions 22a and 23a at even pitch, respectively, the end surfaces
of the core base portions 22a and 23a are abutted against each
other, and the pole cores 20 and 21 are fastened to the shaft 6
facing each other such that the claw-shaped magnetic poles 22 and
23 intermesh.
[0009] Fans 5, each having a plurality of blades 5c in the vicinity
of the outer circumference thereof, are mounted on the end surfaces
of the cylindrical core base portions 22a and 23a at both the ends
of the rotor 7 to be driven in the axial direction thereof. Each
fan 5 has a thin base sheet 5a and the plurality of blades 5c
formed by cutting and raising the base sheet 5a.
[0010] The stator 8 includes a stator core 15, and a stator coil 16
from which alternate current is generated by the change of magnetic
flux from the rotor 7 as the rotor 7 rotates, the stator coil 16
being composed of a conductive wire wound around the stator core
15.
[0011] In the automotive alternator constructed in this manner,
current is supplied from a battery (not shown) to the rotor coil 13
by means of the brushes 10 and the slip rings 9, and the magnetic
flux is generated. The claw-shaped magnetic poles of one pole core
20 are magnetized to N polarities by the magnetic flux, and the
claw-shaped magnetic poles 23 of the other pole core 21 are
magnetized to S polarities. On the other hand, the rotational
torque of the engine is transmitted to the shaft 6 by means of the
belt and the pulley 4, and the rotor 7 is rotated. Thus, a rotating
magnetic field is imparted to the stator coil 16, and electromotive
force is generated in the stator coil 16. This alternating
electromotive force is rectified to direct current by means of the
rectifiers 12, its voltage is regulated by the regulator 18, and
the battery is recharged.
[0012] In the automotive alternator, the rotor coil 13, the stator
coil 16, the rectifiers 12, and the regulator 18 generate heat at
all time while power is generated. To cool heat generated by the
power generation, air intake vents 1a and 2a and air discharge
vents 1b and 2b are disposed in the front bracket 1 and the rear
bracket 2.
[0013] As shown by an arrow in FIG. 24, at a rear-end, external air
is sucked into the case 3 through the air intake vents 2a by means
of the rotation of a fan 5 and cools the rectifiers 12 and the
regulator 18, then cools the rear-end coil end of the stator coil
16 by being deflected centrifugally by the fan 5, and thereafter is
discharged to the outside from the air discharge vents 2b.
[0014] As shown by an arrow in FIG. 24, at a front-end, external
air is sucked into the case 3 through the air intake vents 1a by
the rotation of a fan 5, cools the front-end coil end of the stator
coil 16 by being deflected centrifugally by the fan 5, and
thereafter is discharged to the outside from the air discharge
vents 1b. Further, cooling wind generated by a pressure difference
between the front-end and the rear-end flows from the front-end to
the rear-end through the inside of the rotor 7, and cools the rotor
coil 13.
[0015] In general, automotive alternators, which are auxiliary
machines mounted on vehicles, are required to have a performance to
cope with the requirement for reducing noise outside vehicle and
for making compartment quiet. The alternator includes a rotating
member rotating at the large number of rotation at all times, which
causes a problem of wind noise and magnetic noise. Further, the
alternator, which is a heating member, is increasingly put in
thermally hostile environments by the reduction of a space in which
equipment are mounted. When, for example, the capacity of the fans
5 as a cooling means is increased to cope with the above problem,
noise caused by the fans 5 may be increased. Further, when the
cooling property of the alternator is reduced, an output of the
alternator is decreased.
[0016] As a method of solving the above problem, Japanese
Unexamined Patent Application Publication No. 11-220851 discloses
to prevent an increase in noise by making the number of blades of
fans 5 smaller than the number of claw-shaped magnetic poles. That
is, the method prevents noise caused by the vibration of the
claw-shaped magnetic poles when they rotate from being synchronized
with noise caused by fan blades 5c.
[0017] Incidentally, there is provided the even number of
claw-shaped magnetic poles to alternately form N-poles and S-poles.
Therefore, when the even number of fan blades 5c is used at any one
of a front-end and a rear-end, they include the number of resonance
which is resonated with the number of the claw-shaped magnetic
poles. Particularly, in an automotive alternator whose frequency of
rotation has a considerably wide range, it is a problem that the
above method does not act as a perfect countermeasure for
suppressing interference noise.
SUMMARY OF THE INVENTION
[0018] Accordingly, it is an object of the present invention, which
was made to solve the above problems, to provide a small automotive
alternator having a high output and excellent in a cost performance
without reducing the cooling property thereof even at high
environmental temperature.
[0019] In an automotive alternator according to the present
invention including a case having a plurality of air intake vents
disposed in the axial surface thereof and a plurality of air
discharge vents disposed in the radial surface thereof, a rotor
having a pair of pole cores including claw-shaped magnetic poles
projecting radially externally from the outer circumferential
perimeters thereof at even pitch, respectively, fastened to a shaft
such that the claw-shaped magnetic poles intermesh and rotatably
disposed in the case, the pair of pole cores having a pair of fans,
which include a plurality of blades around the outer circumferences
thereof, and being fastened to the axial end surfaces thereof; and
a stator fastened to the case so as to cover the outer
circumference of the rotor, and having a stator core including a
plurality of slots formed around the inner circumference thereof
facing the rotor and a stator winding accommodated in the slots,
the slots are formed in an even number, each of the claw-shaped
magnetic poles is formed in an even number, and the blades of the
pair of fans are formed in the same odd number, respectively.
[0020] The number of the fan blades may be less than one-half the
total number of the pair of claw-shaped magnetic poles.
[0021] Parts to be cooled are housed in the case at a rear-end and
the amount of wind generated by a fan at a front-end may be larger
than the amount of wind generated by a fan at the rear-end.
[0022] The outlet angle of the fan at the front-end may be larger
than the outlet angle of the fan at the rear-end.
[0023] The outside diameter of the fan at the front-end may be
larger than the outside diameter of the fan at the rear-end.
[0024] Further, the stator winding may include a plurality of
windings in each of which one strand of wire is bent back outside
the slots at the end surfaces of the stator core and wound into
wave winding so as to alternately occupy an inner layer and an
outer layer in a slot depth direction within the slots a
predetermined number of slots apart, and the strand of wire bent
back outside the slots at the end surfaces of the stator core may
be arranged in a circumferential direction, thereby constituting
coil end groups having approximately the same shape.
[0025] Further, the stator winding may include a plurality of
windings in each of which one long strand of wire is bent back
outside the slots at the end surfaces of the stator core and wound
into wave winding so as to alternately occupy an inner layer and an
outer layer in a slot depth direction within the slots a
predetermined number of slots apart, and the turned portions of the
strand of wire bent back outside the slots at the end surfaces of
the stator core may be arranged in the circumferential direction,
thereby constituting coil end groups, the coils ends having
approximately the same shape at said front-end and at the
rear-end.
[0026] Further, the number of the slots may be set to two in each
pole and in each phase.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a sectional view showing a construction of an
automotive alternator according to an embodiment 1 of the present
invention;
[0028] FIG. 2 is a perspective view of a rotor shown in FIG. 1;
[0029] FIG. 3 is a plan view the rotor of FIG. 1 when it is viewed
from a front-end;
[0030] FIG. 4 is a plan view of the rotor of FIG. 1 when it is
viewed from a rear-end;
[0031] FIG. 5 is a perspective view showing a stator of the
automotive alternator;
[0032] FIG. 6 is a plan view explaining connections in one stator
winding phase portion in the automotive alternator;
[0033] FIG. 7 is a circuit diagram of the automotive
alternator;
[0034] FIG. 8 is a view explaining a process for manufacturing a
winding group constituting a stator winding used in the automotive
alternator;
[0035] FIG. 9 is a diagram explaining the manufacturing process for
the winding groups constituting part of the stator winding used in
the automotive alternator;
[0036] FIGS. 10A and 10B are a side elevational view and a plan
view, respectively showing one of strand of wire groups on an inner
layer side constituting part of the stator winding used in the
automotive alternator;
[0037] FIG. 11A and FIG. 11B are a side elevational view and a plan
view, respectively showing one of strand of wire groups on an outer
layer side constituting part of the stator winding used in the
automotive alternator;
[0038] FIG. 12 is a perspective view showing the main portion of
strands of wire constituting the stator winding used in the
automotive alternator;
[0039] FIG. 13 is a diagram explaining arrangement of the strands
of wire constituting part of the stator winding used in the
automotive alternator;
[0040] FIG. 14A and FIG. 14B are a side elevational view and a rear
elevational view, respectively explaining the construction of a
stator core used in the automotive alternator;
[0041] FIG. 15 is a cross sectional view explaining the
manufacturing process for a stator used in the automotive
alternator;
[0042] FIG. 16 is a plan view showing how one of the strand of wire
groups constituting the stator winding used in the automotive
alternator is mounted on the stator core;
[0043] FIG. 17 is a sectional view of the stator used in the
automotive alternator;
[0044] FIG. 18 is a plan view of a rotor of the automotive
alternator according to a second embodiment of the present
invention when it is viewed from a front-end;
[0045] FIG. 19 is a plan view of the rotor when it is viewed from a
rear-end;
[0046] FIG. 20 is a plan view of a rotor of the automotive
alternator according to a third embodiment of the present invention
when it is viewed from a front-end;
[0047] FIG. 21 is a plan view of the rotor when it is viewed from a
rear-end;
[0048] FIG. 22 is a plan view of a rotor of the automotive
alternator according to a fourth embodiment of the present
invention when it is viewed from a front-end;
[0049] FIG. 23 is a plan view of the rotor when it is viewed from a
rear-end;
[0050] FIG. 24 is a sectional view showing a construction of a
conventional, ordinary automotive alternator; and
[0051] FIG. 25 is a perspective view of a rotor shown in FIG.
24.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiment 1
[0052] FIG. 1 is a sectional view showing a construction of an
automotive alternator according to an embodiment 1 of the present
invention; FIG. 2 is a perspective view of a rotor shown in FIG. 1;
FIG. 3 is a plan view the rotor of FIG. 1 when it is viewed from a
front-end; FIG. 4 is a plan view of the rotor of FIG. 1 when it is
viewed from a rear-end; FIG. 5 is a perspective view showing a
stator of the automotive alternator; FIG. 6 is a plan view
explaining connections in one stator winding phase portion in the
automotive alternator; and FIG. 7 is a circuit diagram of the
automotive alternator.
[0053] FIGS. 8 and 9 are diagrams explaining the manufacturing
process for the winding groups constituting part of the stator
winding used in the automotive alternator; FIGS. 10A and 10B are a
side elevational view and a plan view, respectively showing one of
strand of wire groups on an inner layer side constituting part of
the stator winding used in the automotive alternator; FIG. 11A and
FIG. 11B are a side elevational view and a plan view, respectively
showing one of strand of wire groups on an outer layer side
constituting part of the stator winding used in the automotive
alternator; FIG. 12 is a perspective view showing the main portion
of strands of wire constituting the stator winding used in the
automotive alternator; FIG. 13 is a diagram explaining arrangement
of the strands of wire constituting part of the stator winding used
in the automotive alternator; FIG. 14A and FIG. 14B are a side
elevational view and a rear elevational view, respectively
explaining the construction of a stator core used in the automotive
alternator; FIG. 15 is a cross sectional view explaining the
manufacturing process for a stator used in the automotive
alternator; FIG. 16 is a plan view showing how one of the strand of
wire groups constituting the stator winding used in the automotive
alternator is mounted on the stator core; and FIG. 17 is a
sectional view of the stator used in the automotive alternator.
Note that output wires and crossover connections are omitted in
FIG. 5.
[0054] In FIGS. 1 and 2, the automotive alternator is arranged such
that a Lundell-type rotor 7 is rotatably mounted in a case 3
composed of an aluminum front bracket 1 and an aluminum rear
bracket 2 through a shaft 6, and a stator 8 is fastened to the
inner wall surface of the case 3 so as to cover the inner
circumference of the rotor 7.
[0055] The shaft 6 is rotatably supported by the front bracket 1
and the rear bracket 2. A pulley 4 is fastened to an end of the
shaft 6 so as to transmit the rotational torque of an engine to the
shaft 6 through a belt (not shown).
[0056] Slip rings 9 are fastened to the other end of the shaft 6 to
supply current to the rotor 7 and a pair of brushes 10 are
accommodated in a brush holder 11 disposed in the case 3 so as to
be in sliding contact with the slip rings 9. A regulator 18 is
adhered to a heat sink 17 fitted to the brush holder 11 to regulate
the magnitude of the alternating voltage generated by the stator 8.
Rectifiers 12, which are electrically connected to the stator 8,
are mounted in the case 3 to rectify alternate current generated by
the stator 8 to direct current.
[0057] Further, air intake vents 1a and 2a are disposed in the
axial end surfaces of the front bracket 1 and the rear bracket 2,
and air discharge vents 1b and 2b are disposed in the two outer
circumferential shoulder portions of the front bracket 1 and the
rear bracket 2, opposite the radial outside of the front-end and
rear-end coil ends 16 and 16b of the stator winding 16.
[0058] In FIG. 2, the rotor 7 includes a rotor coil 13 for
generating magnetic flux on passage of electric current and a pair
of pole cores 20 and 21 disposed so as to cover the rotor coil 13,
magnetic poles being formed in the pole cores 20 and 21 by magnetic
flux generated in the rotor coil 13. The pair of pole cores 20 and
21 are made of iron and have eight claw-shaped magnetic poles 22
and 23 disposed on the outer circumferential perimeters thereof at
even pitch in a circumferential direction so as to project axially,
respectively, and the pole cores 20 and 21 are fastened to the
shaft 6 facing each other such that the claw-shaped magnetic poles
22 and 23 intermesh. That is, the rotor 7 includes eight poles
cores on each side, namely, it has sixteen (16) claw-shaped
magnetic poles in total. A fan 105 is fastened to the front-end end
surface of the rotor 7, whereas a fan 205 is fastened to the
rear-end end surface of the rotor 7.
[0059] In FIG. 3, the front-end fan 105 is composed of a thin metal
sheet and includes an annular fan base portion 105a and curved
blades 105c formed by cutting and raising a plurality of edges
extending from the outer circumferential edge section of the fan
base portion 105a radially outwardly. The fans 105 is projection
welded in state that fan base portion 105a is abutted against an
end surface of the pole core 20.
[0060] In FIG. 4, the rear-end fan 205 is composed of a thin metal
sheet similarly to the front-end fan 105 and includes an annular
fan base portion 205a and flat blades 205c formed by cutting and
raising a plurality of edges extending from the outer
circumferential edge section of the fan base portion 205 radially
outwardly. The fan 205 is projection welded in the state that the
fan base portion 205a is abutted against an end surface of the pole
core 21.
[0061] In the above construction, the number of the blades of each
of the fans 105 and 205 is set to seven as an odd number which is
smaller than eight which is one-half sixteen, that is, the total
number of the magnetic poles obtained by adding the number of the
claw-shaped magnetic poles 22 of the pole core 20 and the number of
the claw-shaped magnetic poles 23 of the pole core 21.
[0062] As shown in FIG. 5, the stator 8 includes: a cylindrical
stator core 15 composed of a laminated core formed with a number of
slots 15a extending longitudinally at a predetermined pitch in a
circumferential direction; a polyphase stator winding 16 wound onto
the stator core 15; and insulators 19 installed in each of the
slots 15a for electrically insulating the polyphase stator winding
16 from the stator core 15. The polyphase stator winding 16
includes a plurality of windings in each of which one strand of
wire 30 is bent back outside the slots 15a at end surfaces of the
stator core 15 and wound into a wave winding so as to alternately
occupy an inner layer and an outer layer in a slot depth direction
within slots 15a a predetermined number of slots apart. In this
case, the stator core 15 is formed with ninety-six slots 15a at
even pitch so as to house two sets of three-phase stator winding
portions 160 such that the number of slots housing each phase of
the winding portions corresponds to the number of magnetic poles
(sixteen) in the rotor 7. Long, insulated copper wire material
having a rectangular cross section, for example, is used in the
strands of wire 30.
[0063] Next, the winding construction of one phase of a stator
winding group 161 will be explained in detail with reference to
FIG. 6.
[0064] One phase of the stator winding group 161 is composed of
first to fourth winding sub-portions 31 to 34 each formed from one
strand of wire 30. The first winding sub-portion 31 is formed by
wave winding one strand of wire 30 into every sixth slot from slot
number is 1 to 91 so as to alternately occupy a first position from
an outer circumferential side and a second position from the outer
circumferential side inside the slots 15a. The second winding
sub-portion 32 is formed by wave winding a strand of wire 30 into
every sixth slot from slot numbers 1 to 91 so as to alternately
occupy the second position from the outer circumferential side and
the first position from the outer circumferential side inside the
slots 15a. The third winding sub-portion 33 is formed by wave
winding a strand of wire 30 into every sixth slot from slot numbers
1 to 91 so as to alternately occupy a third position from the outer
circumferential side and a fourth position from the outer
circumferential side inside the slots 15a. The fourth winding
sub-portion 32 is formed by wave winding a strand of wire 30 into
every sixth slot from slot numbers 1 to 91 so as to alternately
occupy the fourth position from the outer circumferential side and
the third position from the outer circumferential side inside the
slots 15a. The strands of wire 30 are arranged to line up in a row
of four strands within each slot 15a with the longitudinal
direction of their rectangular cross sections aligned in a radial
direction.
[0065] At a first end of the stator core 15, a first end portion
31a of the first winding sub-portion 31 extending outwards from
slot number 1 and a second end portion 33b of the third winding
sub-portion 33 extending outwards from slot number 91 are joined,
and in addition, a first end portion 33a of the third winding
sub-portion 33 extending outwards from slot number 1 and a second
end portion 31b of the first winding sub-portion 31 extending
outwards from slot number 91 are joined to form two turns of
winding.
[0066] At a second end of the stator core 15, a first end portion
32a of the second winding sub-portion 32 extending outwards from
slot number 1 and a second end portion 34b of the fourth winding
sub-portion 34 extending outwards from slot number 91 are joined,
and in addition, a first end portion 34a of the fourth winding
sub-portion 34 extending outwards from slot number 1 and a second
end portion 32b of the second winding sub-portion 32 extending
outwards from slot number 91 are joined to form two turns of
winding.
[0067] In addition, a portion of the strand of wire 30 of the
second winding sub-portion 32 extending outwards at the first end
of the stator core 15 from slot numbers 61 and 67 is cut, and a
portion of the strand of wire 30 of the first winding sub-portion
31 extending outwards at the first end of the stator core 15 from
slot numbers 67 and 73 is also cut. A first cut end 31c of the
first winding sub-portion 31 and a first cut end 32c of the second
winding sub-portion 32 are joined to form one phase of the stator
winding group 161 having four turns connecting the first to fourth
winding sub-portions 31 to 34 in series.
[0068] Moreover, the joint portion between the first cut end 31c of
the first winding sub-portion 31 and the first cut end 32c of the
second winding sub-portion 32 becomes a bridging connection
connecting portion, a second cut end 31d of the first winding
sub-portion 31 and a second cut end 32d of the second winding
sub-portion 32 become an lead wire (O) and a neutral-point lead
wire (N), respectively.
[0069] Six phases of stator winding groups 161 are similarly formed
by offsetting the slots 15a into which the strands of wire 30 are
wound one slot at a time. Then, as shown in FIG. 7, three phases
each of the stator winding groups 161 are connected into star
connections to form the two sets of three-phase stator winding
portions 160, and each of the three-phase stator winding portions
160 is connected to its own rectifier 12. The rectifiers 12 are
connected in parallel so that the direct-current output from each
is combined.
[0070] Now, the strands of wire 30 constituting the first to fourth
winding b-portions 31 to 34 are each wound into a wave winding so
as to extend out of first slots 15a at end surfaces of the stator
core 15, fold back, and enter second slots 15a six slots away. Each
of the strands of wire 30 is also wound so as to alternately occupy
the inner layer and the outer layer relative to the slot depth
direction (the radial direction) in every sixth slot.
[0071] Turn portions 30a of the strands of wire 30 extend outwards
from the stator core 15 and fold back to form coil ends. The turn
portions 30a which are formed into substantially the same shape at
both axial ends of the stator core 15 are mutually spaced
circumferentially and radially, and arranged neatly in two rows
circumferentially, to form coil-end portions 16a and 16b.
[0072] Next, how the stator 8 is assembled will be explained with
reference to FIGS. 8 to 14.
[0073] First, as shown in FIG. 8, twelve long strands of wire 30
are simultaneously bent in the same plane to form a lightning-bolt
shape. Then, a wire-strand group 35A, shown in FIG. 10, is prepared
by progressively folding the strand at right angles, as indicated
by the arrow in FIG. 9, using a jig. In addition, a wire-strand
group 35B including bridging connections and lead wires, as shown
in FIG. 11, is prepared in a similar manner. The wire-strand groups
35A and 35B are then annealed for ten minutes at 300.degree. C. so
that a parallelepiped core 36 mounted with the wire-strand groups
35A and 35B can be easily formed into an annular shape.
[0074] Moreover, as shown in FIG. 12, each strand of wire 30 is
formed by bending it into a planar pattern in which straight
portions 30b connected by turn portions 30a are lined up at a pitch
of six slots (6P). Adjacent straight portions 30b are offset by a
distance equal to one width (W) of the strands of wire 30 by means
of the turn portions 30a. The wire-strand groups 35A and 35B are
constructed by arranging six wire-strand pairs so as to be offset
by a pitch of one slot from each other, each wire-strand pair
consisting of two strands of wire 30 formed in the above pattern
which are offset by a pitch of six slots and arranged such that
straight portions 30b overlap as shown in FIG. 13. Six end portions
of the strands of wire 30 each extend outwards from first and
second sides at first and second ends of the wire-strand groups 35A
and 35B. Furthermore, the turn portions 30a are arranged so as to
line up in rows on first and second side portions of the
wire-strand groups 35A and 35B.
[0075] The parallelepiped core 36 is prepared as shown in FIG. 14
by laminating a predetermined number of sheets of SPCC material
formed with trapezoidal slots 36a at a predetermined pitch (an
electrical angle of 30.degree.) and laser welding an outer portion
thereof.
[0076] As shown in FIG. 15A, the insulators 19 are mounted in the
slots 36a of the parallelepiped core 36, and the straight portions
of the two wire-strand groups 35A and 35B are inserted so as to
stack up within each of the slots. In this manner, the two
wire-strand groups 35A and 35B are installed in the parallelepiped
core 36 as shown in FIG. 15B. At this time, straight portions 30b
of the strands of wire 30 are housed in lines of four in the radial
direction within the slots 36a and are electrically insulated from
the parallelepiped core 36 by the insulators 19. The two
wire-strand groups 35A and 35B are stacked one on top of the other
when installed in the parallelepiped core 36 as shown in FIG.
16.
[0077] Next, the parallelepiped core 36 is rolled up and its ends
abutted and welded to each other to obtain a cylindrical core 37,
as shown in FIG. 12C. By rolling up the parallelepiped core 36, the
slots 36a (corresponding to the slots 15a in the stator core) take
on a generally rectangular cross-sectional shape, and vent portions
36b of the slots 36a (corresponding to vent portions 15b of the
slots 15a) become smaller than the slot-width dimensions of the
straight portions 30b. Then, the end portions of each of the
strands of wire 30 are connected to each other based on the
connections shown in FIG. 6 to form stator winding groups 161.
[0078] In the automotive alternator constructed in this manner,
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. The claw-shaped magnetic poles 22 of the first pole
core 20 are magnetized with north-seeking (N) poles by this
magnetic flux, and the claw-shaped magnetic poles 23 of the first
pole core 21 are magnetized with south-seeking (S) poles thereby.
At the same time, rotational torque from the engine is transmitted
through the belt and the pulley 4 to the shaft 6, rotating the
rotor 7. Thus, a rotating magnetic field is applied to the
polyphase stator winding 16, generating electromotive force in the
polyphase stator winding 16. This alternating electromotive force
passes through the rectifiers 12 and is rectified to direct
current, the magnitude of the current is regulated by the regulator
18, and the battery is recharged.
[0079] At the rear end, external air is drawn in through the air
intake vents 2a disposed opposite the heat sinks of the rectifiers
12 and the heat sink 17 of the regulator 18, respectively, by
rotation of the fan 205, flowing along the axis of the shaft 6,
cooling the rectifiers 12 and the regulator 18, and is then
deflected centrifugally by the fan 205, cooling the rear-end coil
end group 16b of the polyphase stator winding 16 before being
expelled to the outside through the air discharge vents 2b. At the
same time, at the front end, external air is drawn in axially
through the air intake vents 1a by rotation of the fan 105, and is
then deflected centrifugally by the fan 105, cooling the front-end
coil end group 16a of the polyphase stator winding 16 before being
expelled to the outside through the air discharge vents 1b.
[0080] As described above, according to the embodiment, in the
automotive alternator including the case 3 having the plurality of
air intake vents 1a disposed in the axial surface thereof and the
plurality of air discharge vents 1b disposed in the radial surface
thereof, the rotor 7 having the pair of pole cores 20, 21 including
the claw-shaped magnetic poles 22, 23 projecting radially
externally from the outer circumferential perimeters thereof at
even pitch, respectively, fastened to the shaft 6 such that the
claw-shaped magnetic poles 22, 23 intermesh and rotatably disposed
in the case 3, the pair of pole cores 20, 21 having a pair of fans
105 and 205, which include the plurality of blades 105c and 205c
around the outer circumferences thereof, and being fastened to the
axial end surfaces thereof; and the stator 8 fastened to the case 3
so as to cover the outer circumference of the rotor 7, and having
the stator core 15 including the plurality of slots 15a formed
around the inner circumference thereof facing the rotor 7 and the
stator winding 10 accommodated in the slots 15a, the slots 15a are
formed in an even number, each of the claw-shaped magnetic poles is
formed in an even number, and the blades 105c and 205c of the pair
of fans 105 and 205 are formed in the same odd number,
respectively.
[0081] As a result, vibration of the claw-shaped magnetic poles 23
themselves which is generated when the rotor 7 rotates is not
synchronized with vibration of each of the fans 105 and 205 which
are fastened to the claw-shaped magnetic poles 22 and 23 and have
the blades 105c and 205 and project axially and noise can be
reduced thereby. Further, the front and rear-end blades 105c and
205c are not synchronized with the claw-shaped magnetic poles 22
and 23, respectively because the number of the front-end blades
105c is the same as the number of the rear-end blades 205c, by
which noise can be more reduced. Furthermore, noises, which are
caused by the blades 105c and 205c when they deliver air, are
prevented from having an individually different frequency forward
and rearward of the blades.
[0082] Further, the number of the fan blades 105c and 205c are less
than one-half the total number of the pair of claw-shaped magnetic
poles 22 and 23 (the number obtained by adding the number of the
claw-shaped magnetic poles 22 and the number of the claw-shaped
magnetic poles 23). As a result, the number of the blades 105c and
205c is reduced, permitting the areas of the respective blades 105c
and 205c to be relatively improved. With this construction, the
cooling capability of the fans 105 and 205 can be increased. That
is, the numbers of the blades 105c and 205c of the embodiment are
the same at the front-end and the rear-end and the same number is
seven (7). Namely, the number of each blade is set to an odd number
smaller than eight, that is, one-half the total number of the
magnetic poles of sixteen (16), the odd number (7) being not too
small without reducing the cooling property of the overall
construction of the device.
[0083] Further, the stator winding 16 includes the plurality of
windings 31 to 34 in each of which the one strand of wire 30 is
bent back outside the slots 15a at the end surfaces of the stator
core 15 and wound into the wave winding so as to alternately occupy
the inner layer and the outer layer in the slot depth direction
within the slots 15a a predetermined number of slots 15a apart, and
the strand of wire 30 bent back outside the slots 15a at the end
surfaces of the stator coil 16 is arranged in the circumferential
direction, thereby constituting the coil end groups 16a and 16b
which have approximately the same shape. Accordingly, a coil end
portion, which is arranged neatly over the entire circumference, is
formed, which reduces a ventilation resistance, improves the
cooling property, and improves wind noise.
[0084] The stator winding 16a includes the plurality of windings 31
to 34 in each of which the one long strand of wire 30 is bent back
outside the slots 15a at the end surfaces of the stator core 15 and
wound into the wave winding so as to alternately occupy the inner
layer and the outer layer in the slot depth direction within the
slots 15a a predetermined number of slots 15a apart, and the turned
portion of the strand of wire 30 bent back outside the slots 15a at
the end surfaces of the stator core 15 is arranged in the
circumferential direction, thereby constituting the coil end groups
16a and 16b, and the coil ends have approximately the same shape at
the front-end and the rear-end. As a result, both the coil end
groups 16a and 16b are cooled in good balance, and the temperature
of the stator winding is uniformly and greatly reduced. Further,
the stator winding 16 equally interferes with the blades 105c and
205c at the front-end and the rear-end thereof so as to reduce
interference noise.
[0085] In the embodiment, the number of slots 15a is set to two in
each pole and in each phase. Thus, the number of the slots 15a is
six times the number of the poles so that the frequency of
vibration of the blades 105c and 205c is apart from the frequency
of vibration of the claw-shaped magnetic poles 22 and 23, by which
noise can be more dispersed and reduced. In addition, the number of
the strands of wire 30 extending from the slots 15a is increased,
and hence a noise reduction effect can be more increased.
[0086] Further, the strand of wire 30 constituting the inner
circumferential sides of the coil ends 16a and 16b is inclined in
parallel with each other, permitting an axial air flow in the case
3 to be turned along the inclination of the strand of wire 30. With
this construction, the axial air flow generated by the rotation of
the rotor 7 can be controlled.
[0087] That is, when the strand of wire 30 constituting the inner
circumferential sides of the coil ends 16a and 16b is inclined in a
direction which is obtained by combining the rotating directional
component of the rotor 7 and the axis directional component of
cooling wind, the cooling wind can be promoted to flow axially.
With this construction, the rotor coil 13 is effectively cooled, by
which the temperature of the rotor coil can be can be decreased,
field current can be increased, and an increase in an output can be
expected. In this case, the strand of wire 30 constituting the
inner circumferential sides of the coil ends 16a and 16b is
inclined along the axial flow component of cooling wind, thus wind
noise due to interference can be also reduced.
[0088] On the other hand, when the strand of wire 30 constituting
the inner circumferential sides of the coil ends 16a and 16b is
inclined in the direction which is obtained by combining the
rotating directional component of the rotor 7 and the axis
directional component of cooling wind, the axial flow of cooling
wind can be reduced. With this construction, the amount of wind on
a discharge side is increased in the radial direction and the
cooling property of the coil end disposed to the discharge side can
be improved.
[0089] Note that the blades 105c are not necessarily cut and raised
from the thin base sheet in parallel with the axis of the shaft 6.
Further, the shape and the number of the air intake and discharge
vents 1a and 1b and the positional relationship thereof to the
stator winding 16 are not limited to the illustrated examples so
long as they permit cooling wind from the blades 105c and 205c to
flow smoothly.
Embodiment 2
[0090] FIG. 18 is a plan view of a rotor of the automotive
alternator according to a second embodiment of the present
invention when it is viewed from a front-end; and FIG. 19 is a plan
view of the rotor when it is viewed from a rear-end.
[0091] In the embodiment, a fan 305 is fastened to the end surface
of the rotor 7 at the front-end thereof, whereas a fan 405 is
fastened to the end surface of the rotor 7 at the front-end
thereof.
[0092] In FIG. 18, the front-end fan 305 composed of a thin metal
sheet and includes an annular fan base portion 305a and curved
blades 305c formed by cutting and raising a plurality of edges
extending from the outer circumferential edge section of the fan
base portion 305 radially outwardly. The fan 305 is projection
welded in the state that it is abutted against an end surface of
the pole core 20.
[0093] In FIG. 19, the rear-end fan 405 is composed of a thin metal
sheet similarly to the fan 305 located at the front-end and
includes an annular fan base portion 405a and flat blades 405c
formed by cutting and raising a plurality of edges extending from
the outer circumferential edge section of the fan base portion 405a
radially outwardly. The fan 405 is projection welded in the state
that it is abutted against an end surface of the pole core 21.
[0094] The number of the blades of each of the fans 305 and 405 is
set to an odd number of nine (9) larger than eight (8), that is,
one-half the total number of sixteen (16) of the magnetic poles
obtained by adding the number of the claw-shaped magnetic poles 22
of the pole core 20 and the number of the claw-shaped magnetic
poles 23 of the pole core 21.
[0095] As a result, vibration of the claw-shaped magnetic pole 22
and 23 themselves which is generated when the rotor 7 rotates is
not synchronized with vibration of each of the fans 305 and 405
having the blades 305c and 405c which are fastened to the
claw-shaped magnetic poles 22 and 23 and project axially, by which
noise can be decreased. Further, the front and rear-end blades 305c
and 405c are not synchronized with the claw-shaped magnetic poles
22 and 23, respectively because the number of the front-end blades
305c is the same as the number of the rear-end blades 405c, by
which noise can be more decreased. Furthermore, noises, which are
caused by the blades 105c and 205c when they deliver air, are
prevented from being separately (alternately) generated forward and
rearward of the blades.
[0096] Furthermore, the number of the fan blades 305c and 405 is
larger than one-half the total number of the magnetic poles of a
pair of the claw-shaped magnetic poles 22 and 23 (obtained by
adding the numbers of both the claw-shaped magnetic poles 22 and
23). As a result, the cooling capabilities of the fans 305 and 405
can be improved.
Embodiment 3
[0097] FIG. 20 is a plan view of a rotor of the automotive
alternator according to a third embodiment of the present invention
when it is viewed from a front-end; and FIG. 21 is a plan view of
the rotor when it is viewed from a rear-end.
[0098] In FIG. 20, a front-end fan 505 includes an annular fan base
portion 505a and curved blades 505c formed by cutting and raising a
plurality of edges extending from the outer circumferential edge
section of the fan base portion 505a radially outwardly. Each of
the blades 505c is formed to have a curved surface whose center of
an arc is located externally of the blade.
[0099] In FIG. 21, a rear-end fan 605 includes an annular fan base
portion 605a and flat blades 605c formed by cutting and raising a
plurality of edges extending from the outer circumferential edge
section of the fan base portion 605a radially outwardly,
approximately similarly to the embodiment 1.
[0100] In the embodiment, as to an outlet angle between the outer
circumferential end of each blade and the outer circumferential
circle thereof, the outlet angle A of the front-end fan 505 is
larger than the outlet angle B of the rear-end fan 606. An increase
in the outlet angle B increases the amount of generated wind even
if a blade has the same area. Therefore, in the embodiment, the
amount of wind generated by the front-end fan 505 is larger than
the amount wind generated by the rear-end fan 605.
[0101] In contrast, a wind path in the case 3 is narrow at the
rear-end because internal parts to be cooled such as the rectifiers
12, the regulator 18 and the heat sinks 17 thereof are disposed in
the case 3 at the rear-end, and hence a pressure loss is increased
at the rear-end of the case 3. However, in the embodiment, the
amount of wind generated by the front-end fan 505 is larger than
the amount wind generated by the rear-end fan 605. Accordingly, the
pressure loss of cooling wind at the front-end is made equal to the
pressure loss of cooling wind at the rear-end, noises generated by
the fans being made equal to each other at the front-end and at the
rear-end.
[0102] Further, in the embodiment, the amount of wind generated by
the front-end fan is made larger than the amount of wind generated
by the rear-end fan by making the outlet angle A of the front-end
fan 505 larger than the outlet angle B of the rear-end fan 605.
With this construction, a difference between the amounts of wind
can be realized by a simple construction.
[0103] Note that while each front-end blade 505c of the fan 505 has
the curved surface whose center of arc is located externally of the
blade, it may be formed to have a flat shape because the effect of
the present invention can be obtained when the fan 505 has a large
outlet angle A.
Embodiment 4
[0104] FIG. 22 is a plan view of a rotor of the automotive
alternator according to a fourth embodiment of the present
invention when it is viewed from a front-end; and FIG. 23 is a plan
view of the rotor when it is viewed from a rear-end.
[0105] In FIG. 22, a front-end fan 705 includes an annular fan base
portion 705a and flat blades 705c formed by cutting and raising a
plurality of edges extending from the outer circumferential edge
section of the fan base portion 705 radially outwardly. The fan 705
has an outside diameter .phi.E.
[0106] In contrast, in FIG. 23, a front-end fan 805 includes an
annular fan base portion 805a and flat blades 805c formed by
cutting and raising a plurality of edges extending from the outer
circumferential edge section of the fan base portion 805a radially
outwardly. The fan 705 has an outside diameter .phi.F.
[0107] In the embodiment, the amount of wind generated by the
front-end fan 705 is made larger than the amount of wind generated
by the rear-end fan by making the outside diameter .phi.E of the
front-end fan 705 larger than the outside diameter .phi.F of the
rear-end fan 805. Accordingly, a difference between the amounts of
wind can be realized by a simple construction.
[0108] In the above respective embodiments, the parts to be cooled
such as the rectifiers, the regulator and the like are housed in
the rear-end case. However, the present invention is also
applicable to a type of an alternator in which parts to be cooled
are disposed outside a case and covered with a protection cover or
the like so long as the alternator has a rotor and a stator
constructed similar to those of the above embodiments.
[0109] In each of the above embodiments, copper wire material
having a rectangular cross section is used in the strands of wire,
but the strands of wire are not limited to copper wire material
having a rectangular cross section, and may, for example, be a
copper wire material having a circular cross section. In that case,
formability of the strands of wire is enhanced, facilitating easy
placement and connection of the strands of wire, and improving the
workability. Further, the strands of wire are not limited to copper
wire material, and may, for example, be an aluminium wire
material.
[0110] In each of the above embodiments, four strands of wire are
arranged so as to line up in a row radially within each slot and
the turn portions are arranged to line up in two rows
circumferentially, but six strands of wire may be arranged so as to
line up in a row radially within each slot and the turn portions
are arranged to line up in three rows circumferentially, or eight
strands of wire are arranged so as to line up in a row radially
within each slot and the turn portions are arranged to line up in
four rows circumferentially. Because the more the number of the
strands of wire lined up in a row radially within each slot and the
number of the turn portions lined up circumferentially increase the
more the number of connection portions increase, the present
invention can be used for the construction such that a large number
of the strands of wire are arranged so as to line up in a row
radially within each slot and the turn portions are arranged so as
to line up in a large number of rows circumfetentially.
[0111] In each of the above embodiment, the stator coil have the
lengthy wire 30 folded back outside the slots and threaded in the
slots through inner layers and outer layers alternately in a depth
direction of the slots at every predetermined number of slots, as
explained above; the present invention, however, is not limited
thereto. As an alternative, a plurality of substantially U-shaped
or I-shaped short coil pieces may be inserted from one axial end of
the stator core, and coil piece ends projected at the ends of the
stator core are connected at every predetermined number of coil
pieces thereby to configure a sequential circuit.
[0112] In the automotive alternator according to the present
invention including the case having the plurality of air intake
vents disposed in the axial surface thereof and the plurality of
air discharge vents disposed in the radial surface thereof, the
rotor having the pair of pole cores including the claw-shaped
magnetic poles projecting radially externally from the outer
circumferential perimeters thereof at even pitch, respectively,
fastened to the shaft such that the claw-shaped magnetic poles
intermesh and rotatably disposed in the case, the pair of pole
cores having the pair of fans, which include the plurality of
blades around the outer circumferences thereof, and being fastened
to the axial end surfaces thereof; and the stator fastened to the
case so as to cover the outer circumference of the rotor, and
having the stator core including the plurality of slots formed
around the inner circumference thereof facing the rotor and the
stator winding accommodated in the slots, the slots are formed in
an even number, each of the claw-shaped magnetic poles is formed in
an even number, and the blades of the pair of fans are formed in
the same odd number, respectively.
[0113] Accordingly, vibration of the claw-shaped magnetic poles
themselves which is generated when the rotor rotates is not
synchronized with vibration of each of the fans having the blades
which are fastened to the claw-shaped magnetic poles and project
axially, by which noise can be decreased. Further, the front-end
and rear-end blades are not synchronized with the claw-shaped
magnetic poles, respectively because the number of the front-end
blades is the same as the number of the rear-end blades, by which
noise can be more decreased. Furthermore, noises, which are caused
by the blades, are prevented from having an individually different
frequency forward and rearward of the blades.
[0114] The number of the fan blades is less than one-half the
number of the pair of claw-shaped magnetic poles. Thus, the smaller
number of blades are provided and the area of each blade can be
relatively increased, which can improve the cooling capability.
[0115] In addition, the parts to be cooled are housed in the
rear-end case and the amount of wind generated by the front-end fan
is larger than the amount of wind generated by the rear-end fan.
Accordingly, the pressure loss of cooling wind at the front-end is
made equal to the pressure loss of cooling wind at the rear-end,
and the noises generated by the fans being made equal to each other
at the front-end and at the rear-end.
[0116] The outlet angle of the front-end fan is larger than the
outlet angle of the rear-end fan. Therefore, it is possible to make
the amount of wind generated by the front-end fan larger than the
amount of air generated by the rear-end fan by the simple
construction.
[0117] The outside diameter of the front-end fan is larger than the
outside diameter of the rear-end fan. Accordingly, it is possible
to make the amount of wind generated by the front-end fan larger
than the amount of air generated by the rear-end fan by the simple
construction.
[0118] Further, the stator winding includes the plurality of
windings in each of which the one strand of wire is bent back
outside the slots at the end surfaces of the stator core and wound
into the wave winding so as to alternately occupy the inner layer
and the outer layer in the slot depth direction within the slots a
predetermined number of slots apart, and the strand of wire bent
back outside the slots at the end surfaces of the stator core is
arranged in the circumferential direction, thereby constituting the
coil end groups having approximately the same shape.
[0119] Accordingly, a coil end portion, which is arranged neatly
over the entire circumference, can be obtained, which reduces a
ventilation resistance and improves the cooling property and wind
noise.
[0120] Further, the stator winding includes the plurality of
windings in each of which the one long strand of wire is bent back
outside the slots at the end surfaces of the stator core and wound
into the wave winding so as to alternately occupy the inner layer
and the outer layer in the slot depth direction within the slots a
predetermined number of slots apart, and the turned portions of the
strand of wire bent back outside the slots at the end surfaces of
the stator coil are arranged in the circumferential direction,
thereby constituting the coil end groups, and the coil ends having
approximately the same shape at the front-end and the rear-end.
[0121] Thus, the stator winding interferes with the respective
blades in the same degree at the front-end and the rear-end,
thereby reducing interference noise.
[0122] Further, the number of the slots is set to two in each pole
and in each phase. As a result, the number of slots is six times
the number of poles in a three-phase alternator so that the
frequency of vibration of the fans is apart from the frequency of
vibration of the claw-shaped magnetic poles, by which noise can be
more dispersed and reduced. In addition, the number of the coils
extending from the slots is increased and a noise reduction effect
can be increased.
* * * * *