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 TM 9-8000
Figure 14-3. Typical Starting Motor
with the teeth cut on the rim of the flywheel or with the
the gear ratio may be as high as 25:1 or even 40:1. With
mating half of the dog clutch. The drive must be
double reduction, the gear on the armature shaft does
equipped with an overrunning clutch or some other
not mesh directly with the teeth on the flywheel but with
means of quick disengagement. Owing to limitations of
an intermediate gear, which drives the flywheel driving
size and capacity of the battery, a high-speed starter with
pinion. The double-reduction drive permits the use of a
a high gear reduction is used to obtain the necessary
very small starter running at high speed, but it has the
torque. The great speed reduction required is affected in
disadvantage of requiring a more complicated
the majority of cases by utilizing the flywheel as a driven
mechanism than thesingle-reduction drive.
gear. In some instances, the gear is bolted or shrunk on
c. Overrunning Clutch (Fig. 14-7). Power can be
the flywheel, while in others the gear teeth are cut
directly in the rim of the flywheel itself. The starter is
transmitted through the overrunning clutch in one
mounted on the flywheel housing.
direction only, which prevents the engine from driving the
starter. The shell and sleeve assembly of the clutch is
b. Gear Reduction Starters (Fig. 14-6). The gear
driven by the starter armature shaft. The inner portion,
reduction obtained through the flywheel gear with a
or rotor, is connected to the pinion, which meshes with
single reduction is usually approximately 11:1 or 12:1
the teeth on the engine flywheel. Steel rollers are
(sometimes it is as high as 16:1); that is, the speed of
located in wedge-shaped spaces between the rotor and
the starter armature is 11 or 12 times that of the flywheel.
the shell. Springs and plungers normally hold the rollers
The pinion gear on the armature shaft meshes directly
in position within the wedge spaces. When the starter
with the gear teeth on the flywheel. In some instances,
armature shaft turns, the rollers are jammed between the
however, a double reduction is used, in which case
wedge-shaped surfaces, causing both the inner and the
outer members to rotate as a unit and
TA233576
14-3
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