Alternator with cooling air guide formed by bearing housing...

Electrical generator or motor structure – Dynamoelectric – Rotary

Reexamination Certificate

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Details

C310S062000, C310S065000, C310S089000

Reexamination Certificate

active

06232683

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an alternator comprising a rectifier cooled by external air drawn in through openings in a bracket by the rotation of a fan secured to a rotor.
2. Description of the Related Art
FIG. 9
is a cross section of a conventional automotive alternator,
FIG. 10
is a perspective of the rectifier in
FIG. 9
, and
FIG. 11
is a perspective of the bearing housing portion in FIG.
9
.
This automotive alternator includes: a case
3
comprising an aluminum rear bracket
1
and an aluminum front bracket
2
; a shaft
6
rotatably supported by a first bearing
31
inserted into a bearing housing portion
30
in the rear bracket
1
which constitutes a first bracket and a second bearing
33
inserted into a bearing housing portion
32
in the front bracket
2
which constitutes a second bracket, a pulley
4
being secured to one end of the shaft
6
; a Lundell-type rotor
7
secured to the shaft
6
; a stator
8
secured to an inner wall of the case
3
; slip rings
9
secured to the other end of the shaft
6
for supplying electric current to the rotor
7
; a pair of brushes
10
moving in contact with the slip rings
9
; a brush holder
11
accommodating the brushes
10
; a rectifier
12
electrically connected to the stator
8
for converting alternating current generated in the stator
8
into direct current; a heat sink
17
fitted over the brush holder
11
; and a regulator
18
attached to the heat sink by adhesive for adjusting the alternating current generated in the stator
8
.
The rotor
7
includes: a rotor coil
13
for generating magnetic flux by passing electric current therethrough; and a pole core
14
disposed so as to cover the rotor coil
13
in which magnetic poles are produced by the magnetic flux generated by the rotor coil
13
. The pole core
14
includes a first pole core assembly
21
and a second pole core assembly
22
which mutually interlock. Centrifugal fans
5
for cooling are welded to the axial ends of the first pole core assembly
21
and second pole core assembly
22
.
The stator
8
includes: a stator core
15
; and a stator coil
16
composed of wire wound onto the stator core
15
in which alternating current is generated by changes in the magnetic flux from the rotor coil
13
as the rotor
7
rotates.
The rectifier
12
includes: a positive-side heat sink
24
comprising an arc-shaped heat sink main body
24
a
and a plurality of fins
24
b
standing on the reverse side of the heat sink main body
24
a;
four positive-side diodes
23
composed of molded resin secured by soldering to the upper surface of the positive-side heat sink main body
24
a;
an arc-shaped negative-side heat sink
26
grounded by being secured to the rear bracket
1
; four negative-side diodes
25
composed of molded resin secured by soldering to the negative-side heat sink
26
; and a circuit board
27
for electrically connecting each of the diodes
23
and
25
to the stator coil
16
, the rectifier
12
converting the three-phase alternating current generated by the stator
8
into a direct current.
The positive-side heat sink
24
and the negative-side heat sink
26
are disposed on a generally flat plane in the radial direction of the shaft
6
, and are housed inside the case
3
. The positive-side heat sink
24
and the negative-side heat sink
26
are composed of aluminum which has high thermal conductivity.
In a vehicle alternator of the above construction, a current is supplied by a battery (not shown) through the brushes
10
and slip rings
9
to the rotor coil
13
, whereby magnetic flux is generated, giving rise to a magnetic field and at the same time, the pulley
4
is driven by the engine and the rotor
7
is rotated by the shaft
6
, so that 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 passes through the positive-side diodes
23
and the negative-side diodes
25
of the rectifier
12
and is converted into direct current, the magnitude thereof is adjusted by the regulator
18
, and the battery is recharged.
While the alternator is generating power, the rotor coil
13
, the stator coil
16
, the positive-side diodes
23
, the negative-side diodes
25
, and the regulator
18
are constantly generating heat. For example, in an alternator with a rated output current in the
100
A class, the amount of heat generated is 60 W in the rotor coil
13
, 500 W in the stator coil
16
, a total of 120 W in the positive-side diodes
23
and the negative-side diodes
25
, and 6 W in the regulator
18
. The excessive generation of heat causes deterioration in the performance of the alternator and reduces the working life of the parts.
For that reason, the fans
5
are rotated together with the rotation of the rotor
7
, external air introduced into the case
3
from openings A
1
and A
2
in the case
3
by this rotation flows as indicated by the arrows &agr; and &bgr; in
FIG. 9
, mainly cooling the positive-side heat sink
24
and the positive-side diodes
23
. The external air then flows radially outwards from the fans
5
, cools the end portions of the stator coil
16
in the rear end, and is expelled to the outside through openings B.
External air is also introduced into the case
3
from openings C by the rotation of the fans
5
, and the external air flows as indicated by the arrow &ggr; in
FIG. 9
, cooling the power transistors of the regulator
18
. The external air then flows radially outwards from the fans
5
, cools the end portions of the stator coil
16
in the rear end, and is expelled to the outside through openings D.
Similarly, external air introduced through openings E in the front bracket
2
flows radially outwards from the fans
5
, cooling the end portions of the stator coil
16
in the front end. The external air is then expelled outside the case
3
through openings F.
In an automotive alternator of the above construction, external air flowing into the case
3
through the openings Al flows axially along the cylindrical wall
30
a
of the bearing housing portion
30
and then flows radially outwards, and one problem has been that the cooling efficiency for the positive-side diodes
23
has been poor because the amount of air striking the positive-side heat sink
24
is small and very little contributes to the cooling of the positive-side diodes
23
.
Another problem has been that because the external air flows along flows axially along the curved cylindrical wall
30
a
of the bearing housing portion
30
and the surface area of the cylindrical wall
30
a
is small, the temperature of the first bearing
31
rises and the working life of the first bearing
31
is shortened.
SUMMARY OF THE INVENTION
The present invention aims to solve the above problems and an object of the present invention is to provide an alternator in which the diodes are efficiently cooled and temperature increases in the bearings are suppressed.
To this end, according to the present invention, there is provided an alternator comprising: a case comprising a first bracket and a second bracket; a shaft, one end of the shaft being rotatably supported by a first bearing disposed in a bearing housing portion of the first bracket, and the other end of the shaft being rotatably supported by a second bearing disposed in a bearing housing portion of the second bracket; a rotor secured to the shaft; a stator comprising a stator core secured to an inner wall of the case and a stator coil composed of wire wound onto the stator core; a rectifier for converting alternating current generated in the stator coil into direct current, the rectifier being disposed inside the case and electrically connected to the stator coil; and a fan secured to the rotor for cooling the rectifier by drawing in external air through an opening in the first bracket by rotation of the rotor, the rectifier comprising a heat sink having fins disposed on a rear surface of a heat sink main body, and a number of diodes secu

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