Input and Output Shafts
All transmissions have input shafts and output shafts.
For strength, the shafts are made of heat-treated steel. The
shafts are splined to attach to other parts of the transmis-
sion for power transfer. Every transmission must have sep-
arate input and output shafts, Figure 1-16 and 1-17. Most
automatic transaxles have at least one hollow shaft. The
solid shaft can turn inside the hollow shaft to permit power
transfer to each side of the vehicle. See Figure 1-18.
Planetary Gears
Planetary gears are used in all automatic trans-
missions and transaxles. The term planetary comes from
the resemblance of the gear assembly to the solar system.
The basic planetary gear consists of a central sun gear
surrounded by planet gears that are housed in a planet
carrier. A ring gear with internal teeth surrounds the sun
and planet gears. Figure 1-19 shows the main parts of a
planetary gear assembly. The advantage of the planetary
gear is that the gears remain in mesh at all times. This
prevents gear clash when shifting. Different gear ratios
can be obtained by holding or driving different parts of
the planet gear assembly. Simple planet gears can be
combined into more complex units, such as the one
shown in Figure 1-20. Complex planetary gear sets are
used to obtain many gear ratios.
Holding Members
Holding members are the units that hold or drive the
various parts of the planetary gear assembly to drive the
vehicle. Holding members consist of friction material,
which is similar to that used on manual clutches or brake
shoes, bonded to a metal backing. Clutches and bands are
the most common holding members. Clutches are a series
of flat, ring-shaped plates.
Chapter 1 Introduction to Automatic Transmissions and Transaxles 19
Turbine Impeller
Impeller
Transmission
input shaft
(driven shaft)
Crankshaft
(driving shaft)
Stator
Turbine
Converter cover
Figure 1-14. Engine power flows from the pump, or impeller, to the turbine. The impeller causes the fluid to rotate. Then, the fluid
causes the turbine to rotate. Following the arrows, you will notice that the fluid returning from the turbine strikes the impeller in the
opposite direction of impeller rotation. (General Motors)
Figure 1-13. This sectional view of a torque converter shows
the three main parts: the impeller, the turbine, and the stator. All
modern converters have these three parts arranged in this way.
Modern converters also contain an internal clutch to eliminate
slippage.