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INDEX
PAG
Theory of Operation .......................
22
Gear Trains .............................
22
Simple Planetary .......................
22
Compound Planetary ....................
22
Frictional Units ........................ .
25
Clutches .............................
25
Mechanical Powerflow ....................
25
Hydraulic Component Operation ............
33
Valves & Control Units ..................
33
Hydraulic Circuitry ......................
37
Diagnosis ................................
54
THEORY OF OPERATION
GEAR TRAINS
Simple Planetary Gear Train
A simple planetary gear train (fig. 2M) consists of three
members:
1. A Sun gear.
2. A planet carrier with planet pinion gears.
3. An internal gear.
The sun gear is surrounded by (and meshes with) the
planet pinion gears, which rotate freely on pins attached to a
common bracket called the planet carrier. A ring with teeth
machined on the inside circumference surrounds the assembly
and meshes with the planet pinion gears. This is called the
internal gear, because of its internal teeth.
1. A planetary gear train can be used to increase po
,
and decrease speed (in forward directions) in either
two ways:
a. With the internal gear held and power applied to
sun gear (fig. 3M). As the sun gear turns, the pla
pinions also turn on their pins, and walk aror
inside the internal gear. As the pinions rotate, tl
turn the pinion carrier in the same direction as
sun gear. The planet carrier turns slower than
sun gear-thus providing gear reduction.
b. With the sun gear held and power applied to
internal gear (fig. 4M). As the internal gear to
the planet pinions walk around the sun gear. '
planet carrier then turns slower than the inter
gear-thus providing gear reduction.
Advantages of a Planetary Gear Train
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, occupy less space, and they can trans
mit more tooth load because there is more tooth area in
contact at all times.
2. Planetary gears are always completely in mesh, thus
there is no possibility of tooth damage due to gear clash
or partial engagement.
3. 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.
Operation of a Planetary Gear Train
In describing the operation of the planetary unit, we refer
to pinion "walking" and "idling." When pinions walk they are
moving in or around a member which is held stationary. Thus,
planet pinions walk in the internal gear in the direction
opposite their rotation, and walk around the sun gear in the
same direction they are rotating. The pinions idle whenever
the planet carrier is held stationary and power is applied to the
internal gear or the sun gear.
NOTE: The reduction ratio in `a' is greater than that in
2. A planetary gear train can be used to reverse direct
of rotation when the planet carrier is
-
held station
(fig. SM). In this instance, if power is applied to
sun gear, the planet pinion gears rotate on their resl
tive pins; but since the carrier is stationary, they
merely as idlers, transmitting power to the internal 1
and causing it to rotate in the opposite direction.
In the examples described above, one member has b
held stationary, the power applied to second member,
taken off the third member.
3. A planetary gear train can be used as a coupling
direct mechanical drive when any two members
locked together.
Under this condition movement cannot take p
between the gears and the entire gear train will rotal
a unit.
4. When none of the members are held or locked toget
the planetary gear train will not transmit power; tI
fore it is in neutral.
Compound Planetary Gear Train
The 3-speed automatic transmission combines two sir
