Pontiac FIREBIRD 1972 Service Manual page 904

E-14 1972 PONTIAC SERVICE MANUAL
I
of the sun gear and the planetary gear train func-
tions as a torque increasing, speed-reducing unit.
closed, activating the detent solenoid and causing the
ansmission to downshift at speeds below approximately
mph.
b. The same result can be obtained by holding the
sun gear stationary and applying power to the
internal gear. In this case, rotation of the internal
gear causes the planet pinion gears to rotate on
their respective pins and at the same time rotate
around the sun gear, thus rotating the planet car-
rier at a speed less than that of the internal gear.
The gear train then functions as a torque-increas-
ing, speed-reducing unit.
LANETARY GEAR TRAIN
planetary gear train (Fig. 7E-5) consists of three mem-
:rs:
.
A sun gear.
I.
A planet carrier with four planet pinion gears.
2. A planetary gear train can be used to reverse direc-
tion of rotation when the planet carrier is held sta-
tionary. In this instance, if power is applied to the sun
gear, the planet pinion gears rotate on their respective
pins; but since the carrier is stationary, they act
I.
An internal gear.
he sun gear is surrounded by and meshes with the planet
nion gears, which rotate freely on pins attached to a
)mmon support called the planet carrier. An internal
:ar surrounds the assembly and meshes with the planet
nion gears.
merely as idlers, transmitting power to the internal
gear and causing it to rotate in the opposite direction.
In all of the examples described, one member has been
held stationary, the power applied to another member and
taken off the third member.
DVANTAGES OF A PLANETARY GEAR TRAIN
3 :
A planetary gear train can be used as a coupling for
direct mechanical drive when any two members are
locked together. Under this condition, movement
cannot take place between the gears and the entire
gear train will rotate as a unit.
I . A planetary gear train is compact and sturdy because
the load is distributed over several gears instead of
only two as in the sliding gear-type of gear train.
Planetary gears are smaller and occupy less space.
They can transmit more load because there is more
tooth area in contact at all times.
4. When none of the members are held or locked
together, the planetary gear train will not transmit
power; therefore, it is in neutral.
! Planetary gears are always completely in mesh, thus
there is no possibility of tooth damage due to gear
clash or partial engagement.
OPERATION
).
The common axis for all members of the planetary
train makes the unit more compact and facilitates its
use as a coupling when any two of its members are
locked together.
STARTING ENGINE
1. Place control lever in P or N position. Starter is
inoperative in any other position.
PERATION OF A PLANETARY GEAR TRAIN
2. a. Engine Cold-Depress ac~cierator pedal to floor
once and release (this presets automatic choke
and throttle).
I. A planetary gear train can be used to increase power
and decrease speed in either of two ways:
b. Engine Warm-Hold accelerator pedal down
about half way.
I
3. Turn ignition key clockwise to engage starter, release
a. One method of obtaining speed reduction (torque
multiplication) is to hold the internal gear station-
ary while power
i s
applied to the sun gear. As the
sun gear turns, the planet pinion gears, which are
in mesh with it, rotate on their respective pins.
Since they are also in mesh with the held internal
gear, they must rotate around inside the internal
gear, carrying the planet carrier with them in the
same direction of rotation as the sun gear. The
planet carrier then rotates at a speed less than that
as soon as engine starts.
NOTE: At temperatures below O F , it may be
necessary to hold the accelerator pedal down
slight& while starting.
Do not pump the accelerator at any time. Avoid racing the
engine during the warm-up period. Should the engine