Page 34 - Hydra-matic 6 Speed RWD Technician's Guide (October 2005)

PLANETARY GEARSETS

PLANETARY GEARSETS
Planetary gearsets are commonly used in automatic transmissions in one planetary carrier (68), two sun gears – output carrier front
as the primary method of multiplying the torque, or twisting force, (487) and output carrier rear (489), and two internal gears – output
of the engine (reduction). Planetary gearsets are also used to reverse internal front (495) and output internal rear (497). The front pinion
the direction of rotation, function as a coupling for direct drive, and gears and the rear outer pinion gears share a long pinion shaft, and
provide an overdrive gear ratio. the rear inner pinion gears use a short pinion shaft. The front sun
gear is in constant mesh with the output carrier front pinion gears.
Planetary gearsets are so named because of their physical arrangement. The rear sun gear is in constant mesh with the output carrier rear
All planetary gearsets contain at least three main components: inner pinion gears. The output carrier rear outer pinion gears are in
• a sun gear at the center of the gearset, constant mesh with both the output carrier rear inner pinion gears,
• a carrier assembly with planet pinion gears that rotate around and the rear internal gear (497). The front pinion gears are in
the sun gear and, constant mesh with the output carrier internal front gear (495).
• an internal (ring) gear that encompasses the entire gearset. Also, the output carrier internal gears are splined into the output
shaft, which acts as a part of the output planetary gearset.
The gears are designed such that several gear teeth are always in
contact, or mesh, at the same time. This design distributes the Torque
energy forces over several gear teeth for greater strength and When engine torque is transferred through a gearset, the output
eliminates potential clash that is a common occurrence in manual torque from the gearset can either increase, decrease, or remain the
transmissions when gear teeth go in and out of mesh. Another same. The output torque achieved depends on:
benefit of planetary gearsets is that shafts are generally used for • which member of the gearset provides the input torque,
input and output components and can be arranged on the same axis, • which member of the gearset (if any) is held stationary, and,
thus providing a very compact unit. • which member of the gearset provides the output torque.
The Hydra-matic 6 Speed RWD transmission uses two planetary If output torque is greater than input torque, the gearset is operating
gearsets, an input and output. Figures 25, 26 and 27 show the in reduction (1st, 2nd, 3rd, 4th and Reverse gears). If output torque
gearsets and their respective components. These figures also is less than input torque, then the gearset is operating in overdrive
graphically explain how the planetary gearsets are used to achieve (5th and 6th gear).
each of the transmission's six forward gear ratios and Reverse. Torque vs. Speed
Input Planetary Gearset One transmission operating condition directly affected by input and
The input planetary gearset is comprised of a sun gear (53), a output torque through a gearset is the relationship of torque with
planetary carrier (52) and an internal gear (part of the 4-5-6 output speed. As the transmission shifts from 1st to 2nd through 6th
clutch housing and turbine shaft assembly). The input planetary gear, the overall output torque to the wheels decreases as the speed
gearset is used in all ranges, except 6th gear. of the vehicle increases (when input speed and input torque are held
constant). Higher output torque is needed at low vehicle speed (1st,
Output Planetary Gearset 2nd and 3rd gears) to provide the power to move the vehicle from a
The output planetary gearset is a dual pinion compound gearset that standstill. However, once the vehicle is moving and the speed of the
resembles a combination of two gearsets. This gearset consists of vehicle increases (4th, 5th and 6th gears), less output torque is
three sets of pinion gears, one front and two rear, (inner and outer) required to maintain that speed. This provides for a more efficient
operation of the powertrain.

OUTPUT
OUTPUT OUTPUT CARRIER
INPUT CARRIER CARRIER INTERNAL
INTERNAL INTERNAL ASSEMBLY REAR
GEAR FRONT GEAR (68) GEAR
(495) (497)

INPUT OUTPUT
SUN OUTPUT CARRIER
GEAR CARRIER REAR
(53) FRONT OUTPUT SUN
PINION CARRIER GEAR
GEAR REAR OUTER (489)
INPUT OUTPUT PINION
CARRIER CARRIER GEAR OUTPUT
ASSEMBLY FRONT CARRIER
(52) INPUT OUTPUT REAR INNER
PLANETARY SUN GEAR PLANETARY PINION
GEARSET (487) GEARSET GEAR

Figure 25 25