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14-10
PART
14-3
BOSCH STARTING SYSTEM
250, 302, 351 2V
Section
1 Description
and
Operation
2 Removal and Installation
3 Major Repair Operations
......
,..... . .... .
Page
14-10
14-11
14-11
II
DESCRIPTION AND OPERATION
The Bosch Starter Motor is a series
parallel wound, four pole four brush
machine with solenoid actuated pos-
itive pre-engaged pinion. The main
battery supply is not connected until
the pinion
is
in engagement unless
tooth abutment is experienced. The
drive connection between starter arm-
ature and ring gear is automatically
broken by the overrunning clutch
coupling, which disengages the drive
as soon as the engine speed exceeds
that of the starter.
Closing the mlenoid switching cir-
cuit energises the pull-in and hold-in
solenoid windings. The soft iron plun-
ger is drawn in
moving the engaging
lever which in turn moves
the
drive
assembly towards the ring gear. The
helical splines
on
the armature
shaft
rotate the
pinion slowly
to assist in
engagement.
Should a tooth of the advancing
pinion abut a tooth of the ring gear,
the engaging lever will compress the
helical spring at the pinion until the
switch contacts close. The pinion is
then turned and engages with the ring
gear under the helical spring pressure.
Before the pinion is completely in
mesh the contacts in the solenoid
switch are closed by the action of the
FIG
1.
BOSCH STARTER MOTOR
soft
iron plunger. The starter then
rotates
and cranks the engine. When
the starter rotates, the pull-in wind-
ing is de-energised by the isolation of
its ground connection, providing more
power for cranking.
As the starting speed of the engine
exceeds that of the starter, the pinion
rotates freely and engine acceleration
does not affect the starter. The drive
is pulled back by the tensional helical
spring, but, the pinion remains partly
engaged as long as the starter switch
is
operated.
Once the starter switch is
released, the plunger return spring
moves the pinion to its rest position
and the switch contacts open.
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