Ford Motor Company Transmissions


Ford Motor Company Transmissions

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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