Electric starter motor

Details Electric starter motor Electric starter motor

1999-10-15

2001-05-29

Waks, Joseph (Department: 2834)

Prime-mover dynamo plants

Electric control

Electric-starting motor

C310S083000, C074S00700R

Reexamination Certificate

active

06239503

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electric starter motor provided with a planetary reduction assembly for reducing an rpm of a motor output shaft formed integrally with an armature to transmit to a starter output shaft, and more particularly to a shock absorber mechanism for an electric starter motor for absorbing a shock stress caused by an excessive rotational torque on a loaded side.
2. Description of the Related Art
FIG. 4
is a partial cross-sectional view showing a conventional electric starter motor incorporating a planetary speed reduction device, and
FIG. 5
is a frontal view showing a primary part showing a coupled condition of an internal gear of the planetary reduction assembly in this conventional electric starter motor.
In
FIGS. 4 and 5
, the electric starter motor is composed of a starter motor
3
for generating a rotational torque, a planetary reduction assembly
5
for reducing and outputting an rpm of a motor output shaft
4
of this starter motor
3
, an overrunning clutch
7
engaging with a starter output shaft
6
of this planetary reduction assembly
5
, a pinion
8
integrated with the overrunning clutch
7
and slidably disposed on the starter output shaft
6
, an electromagnetic switch
9
for controlling an electric supply to the starter motor
3
and for pushing the pinion
8
together with the overrunning clutch
7
towards a ring gear
14
of an engine by means of a shift lever
10
, and the like.
The starter motor
3
is composed of a yoke
11
formed into a cylindrical shape having a bottom portion also functioning as an outer frame and a magnetic circuit, a field coil
12
wound around this yoke
11
, an armature
13
disposed within this field coil
12
, a rectifier (not shown) mounted on the motor output shaft
4
, which is a rotary shaft of the armature
13
, a brush (not shown) disposed in sliding contact with this rectifier, and the like. Then, a rear bracket
2
is fitted around an outer circumference of a rear end of the yoke
11
and joined to the yoke
11
to thereby support the rear end of the motor rotary shaft
4
. Also, a front bracket
1
is fitted around an outer circumference of a front end of the yoke
11
and joined to the yoke
11
.
The planetary reduction assembly
5
is composed of a sun gear
15
formed around an outer circumference of a front end of the motor rotary shaft
4
, a plurality of planetary gears
16
meshing with this sun gear
15
and an internal gear
17
meshing with each of the planetary gears
16
.
In the internal gear
17
, a center hole is formed in a central portion of its bottom portion, a rotation stop
19
is formed on an outer circumferential wall surface, and an inner circumferential gear portion
18
is formed into a bottomed cylinder engraved in the inner circumferential wall surface. Then, the internal gear
17
is fitted in the front bracket
1
so as to open on the rear side (on the side of the armature). At this time, the rotation stop
19
is engaged with the front bracket
1
so that the movement of the internal gear
17
in the circumferential direction is restricted.
A discoid flange portion
20
is formed integrally with a rear end of the starter output shaft
6
. Then, a plurality of pins
21
are implanted concentrically at an equiangular pitch on the rear end surface of the flange portion
20
. The planetary gears
16
are supported rotatably to the respective pins
21
. This flange portion
20
, i.e., the starter output shaft
6
is rotatably supported through a bearing
22
fitted in the center hole of the internal gear
17
fixed to the front bracket
1
so that the front end portion of the motor output shaft
4
is rotatably supported through a bearing
23
fitted in the flange portion
20
. Thus, the plurality of planetary gears
16
mesh with the sun gear
15
and the inner circumferential gear portion
18
to thereby constitute a planetary reduction mechanism.
The sun gear
15
rotates together with the motor rotary shaft
4
to transmit the rotation of the motor rotary shaft
4
to each planetary gear
16
. Then, each planetary gear
16
is subjected to the rotation of the sun gear
15
to revolve around the outer circumference of the sun gear
15
while rotating on its axis. The starter output shaft
6
is drivingly rotated by the revolution of the planetary gears
16
.
The overrunning clutch
7
is mounted on the starter output shaft
6
so as to be able to move in the axial direction and such that the rotational motion is transmitted thereto. That is, the overrunning clutch
7
is spline-fitted onto the starter output shaft
6
. The pinion
8
is joined to a front end portion of a sleeve shaft
24
which constitutes the overrunning clutch
7
. The shift lever
10
is mounted rotatably about a pivot portion
10
a
in it s inter mediate portion with its one end being engaged with the overrunning dutch
7
and the other end being coupled to a plunger (not shown) of the electromagnetic switch
9
mounted above the starter motor
3
.
The operation of the thus constructed conventional electric starter motor will now be described.
First of all, before the operation of the starter motor assembly, the shift lever
10
is located in the position shown in
FIG. 4
, the overrunning clutch
7
has not yet been moved and the pinion
8
is not engaged with the ring gear
14
.
Under this condition, when the key switch (not shown) is closed and the electric starter motor is operated, the armature
13
is electrically biased by the electric supply from the electromagnetic switch
9
and is rotated with the biasing force of the field coil
12
. The motor output shaft
4
formed integrally with the armature
13
is drivingly rotated in accordance with the rotation of the armature
13
. Also, the shift lever
10
is driven by the plunger within the electromagnetic switch
9
so that it is rotated about the pivot portion
10
a
in the counterclockwise direction in FIG.
4
. The overrunning clutch
7
is pushed by the rotation of this shift lever
10
. The overrunning clutch
7
and the pinion
8
are moved forward in one piece along the starter output shaft
6
(in the right direction in
FIG. 4
) so that the pinion
8
is engaged with the ring gear
14
.
At this time, the rotational torque outputted from the armature
13
is transmitted from the sun gear
15
of the motor output shaft
4
to the planetary gears
16
. Then, the planetary gears
16
are rotated between the sun gear
15
and the inner circumferential gear portion
18
while rotating about the pins
21
; that is, the planetary gears
16
revolve around the sun gear
15
while rotating on their axes. The flange portion
20
that supports the planetary gears
16
rotates at a more reduced speed than the rpm of the motor output shaft
4
by the revolution of the planetary gears
16
and transmits the reduction speed rotational output to the starter output shaft
6
. Then, the starter output shaft
6
rotates the ring gear
14
(crankshaft) at a reduced rpm through the overrunning clutch
7
and the pinion
8
.
In such an electric starter motor, there are some cases where the crankshaft during the driving rotation is coupled with the starter output shaft
6
so that the crankshaft is abruptly stopped or where the starter output shaft
6
during the driving rotation is abruptly coupled with the crankshaft. In such a case, the excessive rotational torque would be abruptly applied to the starter output shaft
6
. Then, after the rotational torque applied to the starter output shaft
6
has been transmitted from the flange portion
20
at one end of the starter output shaft
6
to the planetary gears
16
, it is transmitted through the inner circumferential gear portion
18
to the internal gear
17
and at the same time transmitted through the sun gear
15
to the motor output shaft
4
.
In the conventional electric starter motor, since the internal gear
17
and the front bracket
1
are coupled together by the rotation stop
19
, there is a disadvantage that the shock stress caused b

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