gearset. Three multiple-disk clutches-one sprag, one
roller clutch, and two bandsprovide the reaction
elements required to obtain the desired function of the
compound planetary gearset.
The torque converter smoothly couples the engine
to the planetary gear through oil and hydraulically y
provides additional torque mulitplication when
required. The torque converter consists of a pump
(driving member), a turbine (driven member), and a
reaction member, known as a stator.
The compound planetary gearset gives three foward
ratios and one reverse. Changing of the gear ratios is
fully automatic in relation to vehicle speed and load.
Planetary gears are used in the Hydra-Matic 400
transmission as a basic means of multiplying the torque
from the engine. The name is derived from the physical
arrangement of the gears. They are always in mesh and
thus cannot clash like other gears that go in and out of
mesh. The gears are so designed so several teeth are in
mesh or in contact at one time. This distributes the forces
over several teeth at one time for greater strength.
Because the shafts generally used with planetary gear
trains can be arranged on the same centerline, a compact
system can be obtained.
A planetary gear train consists of a center or sun
gear, an internal or ring gear, and a planetary carrier
assembly which includes and supports the smaller
planet gears or pinions (fig. 7-12). A planetary gearset
can be used to increase speed increase torque, reverse
the direction of rotation, or function as a coupling for
direct drive. Increasing the torque is known as operating
in reduction because there is always a decrease in the
speed of the output member proportional to the increase
in the output of torque. This means that with a constant
input speed, the output torque increases as the output
Reduction can be obtained in several ways. In a
simple reduction, the sun gear is held stationary, and the
power is applied to the internal gear in a clockwise
direction. The planetary pinions rotate in a clockwise
direction and walk around the stationary sun gear, thus
rotating the carrier assembly clockwise in reduction
Direct drive results when any two members of the
planetary gear train rotate in the same direction at the
same speed. In this condition, the pinions do not rotate
on their pins but act as wedges to lock the entire unit
together as one rotating assembly.
To obtain reverse, restrain the carrier from turning
freely and power is applied to either the sun or the
internal gear. This causes the planet pinions to act as
idlers, thus driving the output member in the opposite
Figure 7-12.Planetary gearset.