Chevrolet Light Duty Truck 1973, Руководство по обслуживанию

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6 Y - 5 4 ENGINE ELECTRICAL
9s. It performs two functions in the starting system. First,
it is used to provide a circuit of short length and low
resistance between the battery and motor. Since the
motor amy draw several hundred amperes during
operation, heavy cables of short length are needed to
reduce the voltage drop in the circuit.
If a solenoid switch were not used and the high motor
currents were carried directly through the start switch,
cables of excessive size would be required to limit the
voltage drop to an acceptable value.
Since the start switch is usually some distance from the
battery and solenoid switch, the long leads connected to
the switch can be of reasonable size since they conduct
only the small current drawn by the solenoid switch
winding (Fig. 10s).
Fig. 9 s — S o le n o id C ross S e c tio n
Fig. 10s—Start Switch Circuit (Typical)
Second, when the start switch is closed, the solenoid
moves the pinion into mesh, and the cranking cycle
begins. When the start switch is opened, the cranking
cycle ends. The neutral safety switch in this type of
circuit is closed only when the transmission shift lever is
in the proper position, thereby preventing cranking of
the engine with the transmission in gear.
The solenoid switch consists basically of two windings
mounted around a hollow cylinder containing a
moveable core or plunger (Fig. 9s). A shift lever is
connected to the plunger. When the push rod and contact
disc is pushed into firm contact with the battery and
motor terminals of the solenoid, with the motor windings
connected directly to the battery, cranking takes place.
The two windings in the solenoid are called the hold-in
winding and the pull-in winding (Fig. 1 Is).
The hold-in winding contains many turns of fine wire
and the pull-in winding the same number of turns of
larger wire. When the start switch is closed, current flows
from the battery to the solenoid (S) terminals, through
the hold-in winding to ground, and then back to the
battery. Current also flows through the solenoid (M)
terminal and then through the motor windings to the
ground.
The magnetism created by each winding adds together to
form a strong magnetic field that attracts the plunger
into the core. Plunger movement shifts the pinion into
mesh with the ring gear and also moves the contact disc
to close the circuit between the solenoid battery (B) and
Motor (M) terminals. With the motor windings
connected directly to the battery through the contact disc,
cranking takes place.
The pull-in winding operates to assist the hold-in
winding in pulling the plunger into the core. Once the
Fig. 11s—Solenoid Windings
SHIFT LEVER
(NOT A PART OF SOLENOID)
CONTACTS
HOLD-IN WINDING
PULL-IN WINDING
LIGHT DUTY TRUCK SERVICE MANUAL