Line Pressure Control

• When an input torque signal equivalent to the engine drive force is sent from the ECM to the TCM, the TCM controls the line pressure solenoid valve.
• This line pressure solenoid controls the pressure regulator valve as the signal pressure and adjusts the pressure of the operating oil discharged from the oil pump to the line pressure most appropriate to the driving state.
  Fig 1: Line Pressure Control System Diagram

  Courtesy of NISSAN MOTOR CO., U.S.A.

Line Pressure Control is Based On The TCM Line Pressure Characteristic Pattern

• The TCM has stored in memory a number of patterns for the optimum line pressure characteristic for the driving state.
• In order to obtain the most appropriate line pressure characteristic to meet the current driving state, the TCM controls the line pressure solenoid current value and thus controls the line pressure.

Normal Control

• Each clutch is adjusted to the necessary pressure to match the engine drive force.
  Fig 2: Line Pressure Graph (Normal Control)

  Courtesy of NISSAN MOTOR CO., U.S.A.

Back-up Control (Engine Brake)

• When the select operation is performed during driving and the A/T is shifted down, the line pressure is set according to the vehicle speed.
  Fig 3: Line Pressure Graph (Back-Up Control)

  Courtesy of NISSAN MOTOR CO., U.S.A.

During Shift Change

• The necessary and adequate line pressure for shift change is set. For this reason, line pressure pattern setting corresponds to input torque and gearshift selection. Also, line pressure characteristic is according to engine speed, during engine brake operation.
  Fig 4: Line Pressure Graph (During Shift Change)

  Courtesy of NISSAN MOTOR CO., U.S.A.

At Low Fluid Temperature

• When the A/T fluid temperature drops below the prescribed temperature, in order to speed up the action of each friction element, the line pressure is set higher than the normal line pressure characteristic.
  Fig 5: Line Pressure Graph (At Low Fluid Temperature)

  Courtesy of NISSAN MOTOR CO., U.S.A.