Starting Motor
Illustration 4
g01357162
(1) Field
(2) Solenoid
(3) Clutch
(4) Pinion
(5) Commutator
(6) Brush assembly
(7) Armature
The starting solenoid (2) is an electromagnetic switch
that performs the following basic operations:
• The starting solenoid (2) closes the high current
starting motor circuit with a low current start switch
circuit.
• The starting solenoid (2) engages the pinion of the
starting motor (4) with the ring gear.
Solenoid (2) has windings (one or two sets) around a
hollow cylinder. A plunger that is spring loaded is
inside the cylinder. The plunger can move forward
and backward. When the start switch is closed and
electricity is sent through the windings, a magnetic
field (1) is made. The magnetic field (1) pulls the
plunger forward in the cylinder. This moves the shift
lever in order to engage the pinion drive gear with the
ring gear. The front end of the plunger then makes
contact across the battery and motor terminals of
solenoid (2). Next, the starting motor begins to turn
the flywheel of the engine.
When the start switch is opened, current no longer
flows through the windings. The spring now pushes
the plunger back to the original position. At the same
time, the spring moves the pinion gear away from the
flywheel.
When two sets of solenoid windings are used, the
windings are called the hold-in winding and the pull-in
winding. Both sets of windings have the same
number of turns around the cylinder, but the pull-in
winding uses a wire with a larger diameter. The wire
with a larger diameter produces a greater magnetic
field (1). When the start switch is closed, part of the
current flows from the battery through the hold-in
windings. The rest of the current flows through the
pull-in windings to the motor terminal. The current
then flows through the motor to ground. Solenoid (2)
is fully activated when the connection across the
battery and the motor terminal is complete. When
solenoid (2) is fully activated, the current is shut off
through the pull-in windings. At this point, only the
smaller hold-in windings are in operation. The hold-in
windings operate for the duration of time that is
required in order to start the engine. Solenoid (2) will
now draw less current from the battery, and the heat
that is generated by solenoid (2) will be kept at an
acceptable level.
M0064276
15
