Hydraulic Line Pressure Control (Automatic gearbox - JF403E)

Hydraulic Line Pressure Control

During engine braking and changing shift range, i.e, from ’D’ to ’2’ position, the line pressure is automatically set higher.

To reduce shock when shifting takes place, line pressure is automatically set lower. After shifting has taken place, the ECU automatically sets the line pressure back to normal.

The ECU has in its memory the ideal time for shifting gears and it measures the actual shift time every time a shift takes place. It then compares this with the ideal time. To reduce gear shifting shock, the ECU sets the gear shift time back. If the actual time is longer or shorter than the ideal time the ECU will adjust the timing accordingly.

When the transmission fluid temperature is below 40C, the line pressure is set lower than normal, but if the transmission fluid temperature is below -10C the line pressure is set at the maximum.

When shifting from ’N’ or ’P’ to ’D’ or ’R’, the line pressure is temporarily set to the maximum to accelerate clutch engagement.

Each gear shift is decided by the ECU based on the shift schedule of each shift pattern, according to vehicle speed and throttle opening angle. The ECU then sends signals to shift control solenoids ’A’ and/or ’B’ depending on the gear selected. When the solenoid valves are OFF, pilot pressure in shift valves ’A’ and ’B’ is reduced, allowing the valves to move. The following table shows the condition in which the solenoids are during each shift position.