A means of changing the direction of rotation of
self-propelled automotive vehicles. Whether the
vehicle is the family automobile, an aircraft tow
the drive wheels (forward and reverse)
tractor, a fire truck, or a weapons loader, a great deal
A means of permitting one drive wheel to turn at
more power is required to start the vehicle in motion
a different speed than the other
than to keep it in motion. Also, power requirements
vary with the load on the vehicle. In addition, both
In addition to the basic components of a power
f o r wa r d a n d r eve r s e m ove m e n t s a r e r e q u i r e d .
train, one or more of the following additional
Therefore, some type of speed and power changing
components may also be part of a drive train: fluid
device is required in the power train. This device is the
couplings, torque converters, transfer cases, and
transmission.
auxiliary transmissions.
In a discussion of the transfer of power from the
NOTE: Basic Machines, NAVEDTRA 14037, has
engine to the drive wheels, we must consider the
an entire chapter devoted to the power train, in which
effects of TORQUE and SPEED. Torque is a twisting
most of the components are described and illustrated.
force that tends to produce rotation or torsion. The
As a result, these components are described only
engine power applies this twisting force to the shafts
briefly in this discussion. Emphasis is on those
and other rotating members of the power train.
component that are not adequately covered in Basic
Machines and some of the applications and different
Consider a small gear (10 teeth) keyed to a shaft
arraqngements of power trains in support equipment.
(driving), extending from the crankshaft, and meshed
Therefore, for a better understanding of the functions
with a larger gear (20 teeth), which is keyed to a second
and operations of the components of the power train,
shaft (driven). The driving shaft is parallel to the driven
the appropriate chapter is Basic Machines should be
shaft, and power from the engine applies torque to the
studied in conjunction with this text.
driving shaft. As the driving shaft turns, the teeth of the
Q2-20. What are the components of a basic power
smaller gear apply torque force to the teeth of the larger
train?
gear, which, in turn, apply torque to the driven shaft.
Since the distance from the center to the rim of the
1. Transmission, propeller shaft, universal
larger gear is greater than that of the smaller gear, the
joints, differential, and axles
twisting force or torque applied on the driven shaft is
2. Transmission, propeller shaft, universal
greater than the torque of the driving shaft. Therefore,
joints, axles, and torque converters
the torque applied by the engine has been increased.
3. Torque converter, transfer case, fluid
couplings, and auxiliary transmission
In the process of increasing the torque, something
4. Torque converter, axles, transmission,
must be lost or decreased. It requires two revolutions of
fluid couplings, and transfer case
the small gear (10 teeth) for one revolution of the large
gear (20 teeth), which is a gear ratio of 2 to 1.
TRANSMISSIONS
Therefore, as the torque increases, speed decreases. By
altering the sizes of the gears on either or both shafts,
LEARNING OBJECTIVES: Identify the
almost any combination of speed and torque can be
components of support equipment
obtained, within the capabilities of the engine.
transmissions. Identify procedures for
Basically, this is what a transmission accomplishes by
inspecting, checking, testing, and adjusting
means of gears or other methods.
support equipment transmissions. Identify
NOTE: Basic Machines, NAVEDTRA 14037,
procedures for troubleshooting support
contains detailed information about the types of gears
equipment. Identify procedures for repairing,
and the manner in which gears may be arranged to
removing, and replacing support equipment
change the speed, torque, or direction of rotation of a
transmissions.
shaft.
There are many different types of transmissions;
If the power requirements between the engine and
however, most can be placed into one of two
the drive wheels were relatively constant, a power train
classes--standard and automatic. With a standard
consisting of a drive shaft and some type of clutch to
transmission, the operator must manually shift the
obtain gradual application of the load on the engine
transmission from one speed/torque ratio to another
would be sufficient. Speed could be regulated by the
engine throttle. However, this is not the case with
using a manually operated clutch. With an automatic
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