Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-10-08
2003-06-03
Lam, Thanh (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S090000, C310S254100
Reexamination Certificate
active
06573631
ABSTRACT:
This application is based on Application No. 2000-316514, filed in Japan on Oct. 17, 2000, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an automotive alternator, and in particular, relates to an outboard bearing construction for supporting a rotor.
2. Description of the Related Art
As the output of automotive alternators has increased, enlargement of rotors and increases in interior temperature have been promoted, requiring size reductions and high bearing reliability.
FIG. 13
is a longitudinal section of a conventional automotive alternator.
In
FIG. 13
, an inboard bracket
1
and an outboard bracket
2
are made of aluminum, formed into bowl shapes, and are fastened together by fastening bolts and nuts (not shown) with open portions of the bowl shapes facing each other. Cylindrical inboard and outboard bearing boxes
1
a
and
2
a
are formed integrally in central portions of end surfaces of the brackets
1
and
2
. In addition, inboard and outboard ventilation apertures
1
b
and
2
b
are bored through the brackets
1
and
2
at outer circumferential portions of the bearing boxes
1
a
and
2
a.
A shaft
3
is rotatably supported in the brackets
1
and
2
by means of inboard and outboard bearings
4
and
5
disposed inside the bearing boxes
1
a
and
2
a
. A Lundell-type rotor
6
is fixed to the shaft
3
and disposed rotatably inside the brackets
1
and
2
. In addition, a stator
7
is disposed with a first and second end thereof supported by the brackets
1
and
2
so as to surround the rotor
6
.
Slip rings
8
for supplying field current to a field winding in the rotor
6
are fixed to an outboard end of the shaft
3
, and a pair of brushes
9
are housed inside a brush holder
10
disposed inside the brackets
1
and
2
so as to slide in contact with the slip rings
8
.
A pulley
11
and an external fan
12
are fixed to an inboard end portion of the shaft
3
, and in addition, a rectifier
13
electrically connected to the stator
7
for converting alternating current generated in the stator
7
into direct current is mounted inside the outboard bracket
2
.
In conventional automotive alternators constructed in this manner, an electric current is supplied from a battery (not shown) through the brushes
9
and the slip rings
8
to the field winding in the rotor
6
, generating magnetic flux. Magnetic poles are generated by this magnetic flux in claw-shaped magnetic poles on the rotor
6
. At the same time, rotational torque from an engine is transmitted through a belt (not shown) and the pulley
11
to the shaft
3
, rotating the rotor
6
. Thus, a rotating magnetic field is applied to a stator winding
7
a
, generating an electromotive force in the stator winding
7
a
. This alternating-current electromotive force passes through the rectifier
13
and is converted into direct current, charging the battery.
The external fan
2
is rotated and driven together with the rotation of the shaft
3
, forming a cooling air flow in which external air flows in through the outboard ventilation apertures
2
b
, flows through the inside of the brackets
1
and
2
, and is expelled through the inboard ventilation aperture
1
b
, cooling heat-generating parts such as the stator
7
, the rotor
6
, the rectifier
13
, and a voltage regulator (not shown).
Now, as shown in
FIG. 14
, the outboard bearing
5
is constituted by a single-row bearing having a cylindrical inner ring
15
and a cylindrical outer ring
16
, a ball track
17
disposed between the inner ring
15
and the outer ring
16
, and a plurality of balls
18
disposed in the ball track
17
. The inner ring
15
is fixed to the shaft
3
, and the outer ring
16
is fixed to the outboard bearing box
2
a.
Thus, rotational torque from the engine is transmitted through the belt and the pulley
11
to the shaft
3
, and the inner ring
15
, which is fixed to the shaft
3
, is rotated and driven with the shaft
3
. A radial load due to tension applied to the belt is transmitted through the plurality of balls
18
to the outer ring
16
. A load due to the weight of the rotor
6
is also transmitted through the plurality of balls
18
to the outer ring
16
. By passing through the balls
18
, these loads are applied to the outer ring
16
as vibrating loads, repeatedly giving rise to warping in the outer ring
16
. Thus, one problem has been that fatigue failure occurs in the inner ring
15
, the outer ring
16
, and the balls
18
, reducing the life of the outboard bearing
5
.
In order to solve this problem, countermeasures have been taken to raise outer-ring rigidity by increasing the diameter of the bearing, substituting a bearing having a large load capacity, or thickening the wall of the outer ring. However, these countermeasures involve increasing the diameter of the outboard bearing
5
, in other words, increasing the diameter of the outboard bearing box
2
a
, thereby reducing the size of the outboard ventilation apertures
2
b
. Similarly, the size of the rectifier
13
is also be reduced due to a necessity to ensure electrical insulation distance between the outboard bearing box
2
a
and the rectifier
13
.
If the size of the outboard ventilation apertures
2
b
is reduced, the cooling air flow rate cannot be ensured, making the cooling of heat-generating parts such as the rotor
6
, the stator
7
, and the rectifier
13
insufficient, and if the size of the rectifier
13
is reduced, the area of a heat sink on the rectifier is reduced, making the cooling of the rectifier
13
insufficient, and as a result, the temperature of the automotive alternator rises, giving rise to reduced output and a deterioration in the life of component parts due to heat degradation.
Another countermeasure has been proposed in which the outboard bearing is constructed by lining up two single-row bearings, preventing fatigue failure by dividing the load in two. However, in that case, radial clearance in the two single-row bearings may differ, making the shared load in the two single-row bearings unbalanced, and a problem has been that bearing life is reduced.
Moreover, the inboard bearing
4
is constituted by a single-row bearing in a similar manner to the outboard bearing
5
, but because the heat-generating parts such as the rectifier
13
and the voltage regulator are disposed at the outboard bracket
2
end, there is ample clear space on the outer circumferential side of the inboard bearing
4
, and it is not necessary to ensure electrical insulation distance between a bearing box and a rectifier. Thus, it is possible to adopt a bearing having enlarged outside diameter, load capacity, or outer-ring wall thickness for the inboard bearing
4
. Consequently, in an automotive alternator, countermeasures against fatigue failure are more important in the outboard bearing
5
, which is where the heat-generating parts such as the rectifier
13
and the voltage regulator are disposed.
In conventional automotive alternators, because the outboard bearing
5
is constituted by a single-row bearing, one problem has been that warping is applied repeatedly, giving rise to fatigue failure in the outboard bearing
5
, thereby reducing bearing life.
Fatigue failure in the outboard bearing
5
can be suppressed by adopting countermeasures in which rigidity is raised by increasing the diameter or the load capacity of the outboard bearing
5
, or by thickening the wall of the outer ring. However, such countermeasures lead to reductions in the size of the outboard ventilation apertures
2
b
and the rectifier
13
, increasing the temperature of the automotive alternator, and another problem has been that these countermeasures give rise to reduced output and a deterioration in the life of component parts due to heat degradation.
SUMMARY OF THE INVENTION
The present invention aims to solve the above problems and an object of the present invention is to provide an automotive alternator enabling the suppression of reductions in output and det
Adachi Katsumi
Asao Yoshihito
Lam Thanh
Mitsubishi Denki & Kabushiki Kaisha
Sughrue & Mion, PLLC
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