Transmission Ranges And Shift Lever Positions - Jeep 200 Cherokee Service Manual

21 - 236 AW–4 AUTOMATIC TRANSMISSION
DESCRIPTION AND OPERATION (Continued)
The pressure created in the fluid is equal to the force
applied, divided by the piston area. If the force is 100
lbs., and the piston area is 10 sq. in., then the pres-
sure created equals 10 PSI. Another interpretation of
Pascal's Law is that regardless of container shape or
size, the pressure will be maintained throughout, as
long as the fluid is confined. In other words, the
pressure in the fluid is the same everywhere within
the container.
Fig. 32 Pressure on a Confined Fluid
FORCE MULTIPLICATION
Using the 10 PSI example used in the illustration
(Fig. 33), a force of 1000 lbs. can be moved with a
force of only 100 lbs. The secret of force multiplica-
tion in hydraulic systems is the total fluid contact
area employed. The illustration, (Fig. 33), shows an
area that is ten times larger than the original area.
The pressure created with the smaller 100 lb. input
is 10 PSI. The concept "pressure is the same every-
where" means that the pressure underneath the
larger piston is also 10 PSI. Pressure is equal to the
force applied divided by the contact area. Therefore,
by means of simple algebra, the output force may be
found. This concept is extremely important, as it is
also used in the design and operation of all shift
valves and limiting valves in the valve body, as well
as the pistons, of the transmission, which activate
the clutches and bands. It is nothing more than
using a difference of area to create a difference in
pressure to move an object.
PISTON TRAVEL
The relationship between hydraulic lever and a
mechanical lever is the same. With a mechanical
lever it's a weight–to–distance output rather than a
pressure–to–area output. Using the same forces and
areas as in the previous example, the smaller piston
(Fig. 34) has to move ten times the distance required
to move the larger piston one inch. Therefore, for
every inch the larger piston moves, the smaller pis-
Fig. 33 Force Multiplication
ton moves ten inches. This principle is true in other
instances also. A common garage floor jack is a good
example. To raise a car weighing 2000 lbs., an effort
of only 100 lbs. may be required. For every inch the
car moves upward, the input piston at the jack han-
dle must move 20 inches downward.
Fig. 34 Piston Travel
TRANSMISSION RANGES AND SHIFT LEVER
POSITIONS
The AW–4 transmission has six ranges and shift
lever positions. Park, Reverse and Neutral are con-
ventional and mechanically operated. The 1–2, 3 and
D ranges provide electronically controlled shifting.
The 1–2 position provides first and second gear
only. The 3 position provides first, second and third
gear.
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