Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-02-28
2001-02-06
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S058000, C310S06800R, C165S047000, C165S080300
Reexamination Certificate
active
06184600
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an automotive alternator mounted to an automotive engine and to a heat sink installed on a rectifier therein.
BACKGROUND ART
FIG. 12
is a cross-section showing an example of a conventional automotive alternator. The alternator in
FIG. 12
includes: a case
3
consisting of an aluminum front bracket
1
and an aluminum rear bracket
2
; a shaft
6
disposed in the case
3
so as to rotate freely by means of bearings to one end of which a pulley
4
is secured; a Lundell-type rotor
7
secured to the shaft
6
and housed in the case
3
; fans
5
secured to both ends of the rotor
7
; a stator
8
secured to the inner wall of the case
3
so as to surround the rotor
7
; 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
disposed in the case
3
so as to slide 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 rectifying 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 regulating the magnitude of the alternating current generated in the stator
8
.
The regulator
18
is constructed by mounting onto a ceramic board power transistors for controlling the excitation current flowing to the rotor
7
and other control circuits. Then, the heat sink
17
, which has a plurality of fins, is fixed to the reverse side of the ceramic board (the side on which the power transistors and control circuits are not mounted) using adhesive, so as to radiate heat generated by the power transistors.
As shown in
FIGS. 13 and 14
, the rectifier
12
includes a positive-side heat sink
24
to which a plurality of positive-side diodes
23
functioning as unidirectional conducting elements are joined, and a negative-side heat sink
26
to which a plurality of negative-side diodes
25
functioning as unidirectional conducting elements are joined, and a circuit board
27
. The positive-side and negative-side heat sinks
24
,
26
each has a plurality of straight fins
24
a
,
26
a
projecting perpendicular to the shaft
6
and extending parallel to the shaft
6
. For example, twenty of these fins
24
a
,
26
a
may be provided having an average thickness of 1.3 mm in the direction of projection, a pitch of 2.5 mm, and a projecting height of 14 mm. The plurality of diodes
23
,
25
are joined with predetermined spacing by soldering to the surfaces of the heat sinks
24
,
26
, respectively, parallel to the shaft
6
on the opposite side to the side on which the fins
24
a
,
26
a
are disposed. The heat sinks
24
,
26
are assembled so that the backs of each of the diodes
23
,
25
are positioned opposite each other in the radial direction. Leads
23
a
,
25
a
of the paired positive-side and negative-side diodes
23
,
25
are gathered together in one place at the connecting terminals
27
a
of the circuit board
27
, and are each connected to the output terminals
16
a
of the stator coil
16
, so as to rectify three-phase alternating current into direct current. Furthermore, heat generated by the diodes
23
,
25
due to power generation is radiated from the fins
24
a
,
26
a
disposed on the heat sinks
24
,
26
.
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 formed by the magnetic flux generated by the rotor coil
13
. The pole core
14
includes a first pole core body
21
and a second pole core body
22
which mutually interlock.
The stator
8
includes: a stator core
15
; and a stator coil
16
composed of wire wound onto the stator core
15
in which an alternating current is generated by changes in the magnetic flux from the rotor coil
13
as the rotor
7
rotates.
In a conventional automotive alternator constructed in the above manner, 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, and at the same time, the rotational torque of the engine is transferred to the shaft by means of the pulley
4
, rotating the rotor
7
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 rectifier
12
and is rectified into direct current, the magnitude thereof is regurated by the regulator
18
, and the battery is recharged.
Now, the rotor coil
12
, the stator coil
16
, the rectifier
12
, and the regulator
18
constantly generate heat during power generation. In an alternator with a rated output current in the 100 A class, the amount of heat generated in the rotor coil
12
, the stator coil
16
, the rectifier
12
, the regulator
18
is 60 W, 500 W, 120 W, and 6 W, respectively.
Intake openings
1
a
,
2
a
and exhaust openings
1
b
,
2
b
for allowing ventilation generated by the fans
5
disposed on the rotor
7
to pass through are bored in the front bracket
1
and the rear bracket
2
. Thus, in the rear end, due to the rotation of the fans
5
(rotor
7
), air from outside flows into the case
3
through the intake openings
2
a
disposed opposite the heat sinks
17
,
24
,
26
, flows through the heat sinks
17
,
24
,
26
and cools the rectifier
12
and the regulator
18
. Then that air is redirected centrifugally by the fans
5
, cools the stator coil ends in the rear end and is then discharged to the outside through the exhaust openings
2
b
. In the front end, due to the rotation of the fans
5
, air from outside flows axially into the case
3
through the intake openings
1
a
, then that air is redirected centrifugally by the fans
5
, cools the stator coil ends in the front end, and is then discharged to the outside through the exhaust openings
1
b.
The fins disposed on the heat sinks
17
,
24
,
26
are formed perpendicular to the contact surfaces between the ceramic board and diodes and the heat sinks
17
,
24
,
26
, and temperature increases in the diodes
23
,
25
of the rectifier
12
and the power transistors of the regulator
18
are suppressed by heat exchange with the air flowing between the fins. When the amount of heat generated and the materials used are constant, the value of the temperature increase dt is greatly dependent on the speed v of the air flowing through the heat sinks and the surface area A of the fins, and the relationship between them can be expressed by Expression (1):
dt
∝Q/(A×
v
&agr;
) (1)
Moreover, &agr; is determined by the state of the air flowing through the heat sinks, and is 0.5 if the flow is laminar and 0.8 if the flow is turbulent.
From Expression 1, it can be seen that temperature increases dT can be suppressed by increasing the surface area A of the fins, and in a limited space, this means making the fins thinner and increasing the number of fins. However, although the surface area of the fins can be increased by making the fins thinner and increasing the number of fins, the amount of ventilation passing through decreases, reducing the speed v of the air, and consequently temperature increases cannot be suppressed in this way.
FIG. 15
is a cross-section showing another example of a conventional automotive alternator such as that described in Japanese Patent Laid-Open No. HEI 8-182279,
FIG. 16
is a planar projection of the rear bracket of the automotive alternator shown in
FIG. 15
, and
FIGS. 17 and 18
are a perspective and a plan, respectively, showing a rectifier used in the automotive alternator shown in FIG.
15
.
Apart from the use of a rectifier
30
, the construction of this conventional automotive alternator is the same as for the conventional automotive alternator shown in FIG.
12
.
The rectifier
30
used in this conventional automotive alternator includes a
Adachi Katsumi
Asao Yoshihito
Nakashima Shinji
Mitsubishi Denki & Kabushiki Kaisha
Nguyen Tran
Sughrue Mion Zinn Macpeak & Seas, PLLC
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