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The
circuitry and components used by Ford Motor Company to control their
transmissions varies with transmission models and applications. Although there
are some similarities across models, the common systems should be looked at
individually.
Ford AOD-E Controls The AOD-E is a fully automatic four-speed transmission
with electronic shifting, torque converter control, and line pressure
controls. This transmissions is identical to an AOD except it no longer uses a
split-torque converter and its operation is controlled by the electronic engine
control's (EEC) electronic control assembly (ECA). Input sensors provide
information to the ECA, which, in turn, controls actuators. Actuators control
transmission operation.
The
engine control system consists of the ECA, sensors, switches, and solenoids. It
also has self-diagnostic capabilities. The engine sensors supply the ECA with
the information necessary to determine engine operating conditions, through
voltage signals. The ECA will then send out electrical signals to control
air/fuel ratio, idle speed, emission controls, ignition timing, and transmission
solenoids.
The
ECA uses logic to control shift scheduling, shift feel, and converter lockup,
and relies on information from the engine control system, through such sensors
as the MAP and TPS, as well as information from the transmission to determine
the optimum shift timing. Information about the operation of the transmission is
received by the ECA through signals from an output shaft sensor (OSS), vehicle
speed sensor (VSS), transmission oil temperature (TOT) sensor, and a manual
lever position sensor (MLPS).
The
transmission control system uses four solenoids for control of operation. One
solenoid, the MCCC solenoid, is used for modulated converter clutch control.
Another, the EPC solenoid, is used to control hydraulic pressures throughout the
transmission. The remaining two solenoids are shift solenoids.
The
EPC solenoid replaces the conventional TV cable setup to provide changes in
pressure in response to engine load. This solenoid is a variable force solenoid
(VFS) and contains a spool valve and spring. To control fluid pressure, the ECA
sends a varying signal to the solenoid. This varis the amount the solenoid will
cause the spool valve to move. When the solenoid is off, the spring tension
keeps the valve in place to maintain maximum pressure. As more current is
applied to the solenoid, the solenoid moves the spool valve more, which moves to
uncover the exhaust port more, thereby causing a decrease in pressure. The shift
solenoids offer four possible on/off combinations to control fluid to the
various shift valves.
Ford AXOD-E Controls
The
AXOD-E is an electronically controlled four-speed transaxle. Shift control
solenoids provide gear changes and are controlled by the ECA, as is the
converter lockup clutch solenoid. Five solenoids are mounted on the AXOD-E valve
body to control transmission functions. One solenoid, the MCCC solenoid, is used
for modulated converter clutch control. Another, the EPC solenoid, is used to
control hydraulic pressures throughout the transmission. The remaining three
solenoids are shift solenoids.
The
EPC solenoid replaces the conventional TV cable setup to provide changes in
pressure in response to engine load. This solenoid is a variable force solenoid
and contains a spool valve and spring. To control fluid pressure, the ECA sends
a varying signal to the solenoid. This varies the amount the solenoid will cause
the spool valve to move. When the solenoid is off, the spring tension keeps the
valve in place to maintain maximum pressure. As more current is applied to the
solenoid, the solenoid moves the spool valve more, which moves to uncover the
exhaust port more, thereby causing a decrease in pressure.
The
shift solenoids offer many possible on/off combinations to control fluid to the
various shift valves. These solenoids are on/off solenoids that are normally off
and in the open position. Being open, the solenoid valves allow line pressure to
the bore of the shift valve and keep the shift valve closed. When the shift
solenoids are energized, they block the line pressure and exhaust line pressure
from the valve. This allows the shift valve to open.
Ford A4LD Controls The A4LD is a four-speed automatic transmission with a
lockup torque converter. The engine control system controls the operation of the
lockup converter clutch and the operation of a shift solenoid for third to
fourth gear shifting. Prior to 1987, 3-4 shift was done hydraulically. In 1987,
a electronic 3-4 shift solenoid was added.
This
solenoid is normally off and permits line pressure flow through the solenoid
valve, which inhibits the 3-4 shift. When the ECA receives information that the
time is right to allow the 3-4 shift, the solenoid is energized and the
inhibitor oil is exhausted. This allows the hydraulic shift valve to make the
shift.
Ford 4EAT Controls The 4EAT is a four-speed transaxle that is controlled
both electronically and hydraulically. Input signals from sensors are sent to
the 4EAT control module, the Madza electronic control system (MECS), which
controls the appropriate gear range, shift timing, and converter clutch lockup
timing. The 4EAT control module has self-diagnostic capabilities, a fail-safe
mode, and a warning code display for the main input sensors and solenoid valves.
Four solenoid valves are located in the valve body. These redirect fluid flow
and cause shifting and converter lockup. The 4EAT can be operated in manual or
automatic shift mode. Manual shifting can be selected by the driver through a
switch located on the center console. When the switch is in the NORM position,
the transmission automatically shift gears to achieve maximum fuel economy. Some
model cars have a switch that allows the driver to select in and out of a POWER
range. Selection of the POWER range, cause a delay in the shift timing to
provide for maximum acceleration.
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