Chapter 30 Engine Starting Systems 509
speed and higher torque output to the fl ywheel.
More constant engine cranking speeds are produced
by a reduction starter.
12-Volt Starting Motor Types
Starting motors are classifi ed by type of pin-
ion gear engagement. There are two main 12-volt
starter types: movable pole shoe starting motors
and solenoid-actuated starting motors. Both types
are illustrated in Figure 30-15.
A movable pole shoe starting motor uses a drive
yoke to move the pinion gear into contact with
the fl ywheel gear. The drive yoke is hinged on the
starter frame and links a movable pole shoe to the
pinion gear, Figure 30-15A.
When the starter is activated, the magnetic fi eld of
the motor pulls the movable pole shoe downward.
Overrunning clutch
Drive yoke
or lever
Holding coil
Pivot pin
Movable
pole shoe
Return
spring
Drive end
frame
Pinion gear
Overrunning clutch
Overrunning clutch
Pinion gear
Drive end
frame
Shift fork
Plunger
Return spring
Pivot pin
Field frame
Starting Motor with Movable Pole Shoe
Starting Motor with Solenoid
Armature
Commutator
end frame
Brush assembly
Plunger contact
disc
Motor feed
terminal
Bypass
ignition
terminal
Commutator
end frame
Field brush
Brush spring
Ground brush
Field coil
Armature
Pole shoe
Field
frame
Field coil
Solenoid
windings
Figure 30-15. Compare two common types of 12-volt starting motors. (Ford)