With the introduction of the AOD
transmission. Ford became the first manufacturer to offer an automatic
transmission with a built-in overdrive. The AOD is a 4-speed
transmission that uses the Ravigneaux gear train.
Another feature of the AOD is the
split-torque-type torque converter. This arrangement consists of two
input shafts driven by the converter. One of these shafts relays torque
into the transmission through the normal hydraulic action of a converter
and the other shaft provides a mechanical link from the engine to the
gear train when the transmission is operating in third and fourth gears.
The AOD uses the common ring gear as the
output member. Two sun gears are used, a small one called the forward
sun gear and a larger one called the reverse sun gear. The planetary
gearset has two sets of planetary pinions gears, three long and three
short ones. The planetary pinion gears are able to rotate on their own
shafts while sharing the common planetary carrier.
The AOD uses four multiple-disc clutches,
two one-way clutches, and two bands to obtain the various gear ranges.
The forward sun gear is driven by the turbine shaft when the forward
clutch is applied. The reverse sun gear is driven by the turbine input
shaft when the reverse clutch is applied and is held, during overdrive,
by the overdrive band. The reverse sun gear also can be held by applying
the intermediate clutch in second, third, and fourth gears.
The single planetary carrier assembly can
be held by either the low/reverse band or the low one-way clutch. The
long pinion gears are in constant mesh with the ring gear, the reverse
sun gear, and the short pinion gears. The short pinion gears are in
constant mesh with the forward sun gear and the long pinions.
The short pinions do not mesh with the
ring gear but can drive it through the long pinion gears. The ring gear
is splined to a flange on the output shaft and the ring gear is always
the output member.
Input Devices The AOD uses a torque
converter that splits power flow from the engine. The converter drives
two input shafts to provide both a hydraulic and mechanical input into
the transmission. A typical input shaft from the converter's turbine
hydraulically drives the forward clutch drum. An additional input shaft
linked to the converter cover mechanically links the output of the
engine to the direct clutch. The amount of input from either or both
sources varies according to the operating gear. When the transmission is
operating in first, second, and reverse gears, 100 percent of the input
is delivered hydraulically by the turbine shaft. When operating in third
gear, the gear train receives approximately 40 percent of its input from
the turbine shaft and 60 percent is delivered through the mechanical
linkage. In fourth gear, all of the input to the gear train is through
the mechanical linkage.
Regardless of the input into the
transmission, the gear train receives power through the application of
the forward, direct, or reverse clutches, which serve as the input
devices for the gear train.