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 TM 9-8000
PART FOUR
POWER TRAINS
CHAPTER 19
INTRODUCTION TO POWER TRAINS
Section I. PURPOSE
Transmission power takeoffs are available in several
19-1. Providing Power to Propel Vehicle. One
different designs: a single-speed, two-gear model in
important function of the power train is to transmit the
which the rotation of the power takeoff shaft is opposite
power of the engine to the wheels. In a simple situation,
to that of the engine; a model having a single speed
a set of gears or a chain could perform this task, but
forward and reverse; and a model having two speeds
automotive vehicles usually are not designed for such
forward and one reverse. Several different mountings
simple operating conditions. They are designed to have
also are available.
great pulling power, move at high speeds, travel in
reverse as well as forward, and operate on rough ground
The same types of power takeoffs also are applied to
as well as on smooth roads. To meet these widely
auxiliary transmissions. Figure 19-2 shows a winch
varying demands, a number of units have been added.
driven off of an auxiliary transmission.
These include clutches, transmissions, auxiliary
transmissions, transfer cases, propeller shafts, universal
Power sometimes is taken off a transfer case. The
joints, final drives, differentials, live axles, devices for
transfer case drive shaft, which is connected to the
transmission, extends through the case, and the power
therein.
takeoff shaft is engaged to it by a dog clutch. This
transfer case has two speeds and a neutral position. It is
19-2.
Providing Power to Operate Accessories
necessary to put the transfer case sliding gear in the
(Power Takeoff). The power train also is designed to
neutral position if the vehicle is to be stationary while the
direct power to the accessories. These branches from
power takeoff is in use. If the power takeoff is needed
the main flow of power are known as power takeoffs.
while the vehicle is in motion, the transfer case may be
They may be connected to the transmission, auxiliary
shifted either into high or low range.
With this
transmission, or transfer case. The simplest type of
arrangement, the power takeoff will work on any speed of
transmission power takeoff is the single-gear, single-
the transmission.
speed type shown in figure 19-1. This unit is bolted over
an opening provided for that purpose at the side of the
When the power takeoff clutch is engaged, the winch
transmission case. This opening is closed by a cover
capstan operates; but the winch drum does not rotate
plate when no power takeoff is used. The opening in the
until the winch clutch is engaged.
transmission case and the power takeoff gear meshes
with a gear on the transmission countershaft. As shown
The several types of power takeoffs have been described
in figure 19-1, the gear slides on the splined main shaft,
as operating winches, but their uses for operating various
off which the power is taken. The shifter shaft, controlled
kinds of hoists, pumps, and other auxiliary power-driven
by a lever in the driver's cab, slides the gear in and out of
machinery are essentially the same.
mesh with the countershaft gear. Because it is driven by
the countershaft, the power takeoff shaft rotates in the
same direction as the engine crankshaft.
19-1
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