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Automatic Transmission (4AT) - Mechanism & Function: Overview Subaru Outback BS

Automatic Trans 1 illustration ~298 words

CONTROL WHEN CRUISE CONTROL IN OPERATION

When the cruise control is operating, shifting control is performed by automatically switching to a shifting map that is suitable for cruise control.

NON-LOCKUP OPERATION

The duty solenoid allows the pilot pressure to be applied to the disengaging end of the valve in the control valve body. The valve then opens the clutch disengaging circuit port to add the lockup operating pressure (torque converter clutch regulating pressure) to the disengaging circuit. Moreover, the valve opens the lockup clutch engaging circuit port and allows the hydraulic fluid in the circuit to flow to the ATF cooler, thus lowering the pressure in the circuit. As a result, the lockup clutch is disengaged due to difference in pressure between both circuits.

This control is performed in all gear positions.

LOCKUP OPERATION

The duty solenoid allows the pilot pressure to be applied to the engaging end of the valve in the control valve body. The valve then opens the clutch engaging circuit port that communicates to the torque converters impeller chamber, allowing high pressure fluid to flow to the lockup clutch. The clutch then engages.

  1. The TCM controls the current to the duty solenoid by gradually changing the current. As a result, the valve also moves gradually, so the clutch engagement pressure increases smoothly. This causes the lockup clutch to become initially in a half-engaged state and then in a fully engaged state, thus preventing shock during engagement.

This control is performed in all gear positions.

OPERATION OF SPORT INDICATOR LIGHT

On starting the engine, the SPORT indicator light illuminates and then goes out as shown in the Normal diagram below. If any problem exists, the light continues flashing as shown in the Abnormal diagram below.

Scheme 7

Scheme 7: OPERATION OF SPORT INDICATOR LIGHT