Chevrolet 1977 light duty truck, Руководство по обслуживанию

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HOLD-IN W IN D IN G
(NOT A PART OF SOLENOID)
Fig. 6 D -9 s -S o le n o id C ross S e ctio n
Fig. 6 D -7 s ~ A rm a tu re A s s e m b ly
D r iv e M e c h a n i s m
The starting m otor drive mechanism (Fig. 6D-8s) is a
roll-type overrunning clutch that is assembled onto the
armature shaft. Through this drive com ponent power is
transm itted from the armature to the engine during the
starting cycle.
The overrunning clutch drive contains a pinion which
is made to move along the shaft by means of a shift lever to
engage the engine ring gear for cranking. A gear reduction
is provided between the pinion and ring gear to meet the
cranking requirem ents of the engine. W ith this gear
reduction, the m otor operates to crank the engine at speeds
required for starting.
The overrunning clutch drive has a shell and sleeve
assembly which is splined internally to m atch the spiral
splines on the arm ature shaft. The pinion is located inside the
shell along with spring-loaded rollers that are wedged against
the pinion and a taper inside the shell. The springs may be
either a helical or accordion type. Four rolls are used. A
collar and spring, located over the sleeve, are the other major
clutch components.
W hen the shift lever is operated by the solenoid, it moves
the collar endwise along the shaft. The spring pushes the
pinion into mesh with the ring gear. If a tooth abutm ent
occurs, the spring compresses until the switch is closed, at
which time the arm ature rotates and the tooth abutm ent is
cleared. The compressed spring then pushes the pinion into
mesh and cranking begins.
Torque is transm itted from the shell to the pinion by the
rolls which are wedged tightly between the pinion and taper
cut into the shell.
When the engine starts, the ring gear drives the pinion
faster than the arm ature and the rolls move away from the
taper, allowing the pinion to overrun the shell. The start
switch should be opened immediately when the engine starts
to avoid prolonged overrun. When the shift lever is moved
back by the return spring, the pinion moves out of mesh and
the cranking cycle is completed.
S O L E N O ID
A sectional view of a typical solenoid is shown in Figure
6D-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 m otor
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 m otor
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.
6D-10s).
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 transm ission 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. 6D-9s). A shift lever is connected to the
plunger. W hen the push rod and contact disc is pushed into
firm contact with the battery and m otor terminals of the
solenoid, with the m otor windings connected directly to the
battery, cranking takes place.
BUSHINGS
SHELL AN D
SLEEVE ASSEMBLY
LOCK WIRE
C L U T C H -----------
PIN IO N AN D
COLLAR ASSEMBLY