Fourth Gear

FOURTH GEAR
The driving force of the turbine shaft is transmitted to the planetary carrier through the 3-4 clutch to rotate it counterclockwise. The large sun gear, however, is locked by the 2-4 brake band and thus does not rotate.
As a result, the internal gear rotates counterclockwise due to the planetary gear set operation. It rotates faster than the third gear and the driving force is transmitted to the driving wheels.
The driving force of the turbine shaft is also is transmitted to the one-way clutch outer race through the forward clutch. The rotation speed of the small sun gear (that of the one-way clutch inner race) is higher than that of the one-way clutch outer race. Thus, one-way clutch 1 freewheels and does not transmit power.
During deceleration, the engaged 3-4 clutch transmits the rotation speed of the internal gear and planetary carrier to the engine side, and engine braking is obtained.





Hydraulic pressure operation
Line pressure (7) generated in the oil pump is adjusted by the pressure regulator valve and transmitted to the manual valve, throttle valve, 1-2 shift valve, 2-3 shift valve, 3-4 shift valve, torque converter clutch control valve, 1-2 accumulator, 2-3 accumulator, and N-D accumulator.
Due to the manual valve position line pressure (7) is transmitted to (1) and (3). Line pressure (1) works on the 1-2 shift valve, 3-4 shift valve, and N-D accumulator, and engages the forward clutch. Line pressure (3) works on the 2-3 shift valve.
With shift solenoid A ON, line pressure (1) is transmitted to (9) due to the 1-2 shift valve operation. Line pressure (9) works on the 1-2 accumulator and 2-4 brake band applied side, engaging the 2-4 brake band.
With shift solenoid B OFF, line pressure (3) is transmitted to (13) due to the 2-3 shift valve operation. Line pressure (13) works on the 2-3 accumulator, and then engages the 3-4 clutch.
With shift solenoid C ON, line pressure (15), which works on the 2-4 brake released side, is drained from the 3-4 shift valve, and line pressure (16), which engages the coasting clutch, is drained from the 3-4 shift valve.
Line pressure (7) driven to the pressure regulator valve is transmitted to torque converter pressure (23) and sent to the torque converter through the torque converter clutch control valve.

Torque converter clutch non operation
With the torque converter clutch solenoid OFF, torque converter pressure (23) is transmitted to (24) due to the torque converter clutch control valve operation, and works on the torque converter front chamber.

Torque converter clutch operation
With the torque converter clutch solenoid ON, torque converter pressure (23) is transmitted to (25) due to the torque converter clutch control valve operation, and works on the torque converter rear chamber. At that moment, torque converter pressure (24) is drained from the torque converter clutch control valve.