Line Pressure System Diagram

Fig 1: Line Pressure System Diagram

Courtesy of KIA MOTORS AMERICA, INC.

Line pressure control based on line pressure characteristic pattern of A/T control unit (TCM)

A/T control unit (TCM) has stored in memory a number of patterns for the optimum line pressure characteristics according to driving conditions.
In order to obtain the most appropriate line pressure characteristic to meet the current driving state, the TCM controls the line pressure solenoid current valve and thus controls the line pressure.
- Normal line pressure control.
  Each clutch is adjusted to the necessary pressure to match the engine drive force.
  
  Fig 2: Normal Line Pressure Control - Line Pressure Characteristic Pattern
  Courtesy of KIA MOTORS AMERICA, INC.
- Back-up control (Engine brake)
  Line pressure according to speed is set during shift down by select operation while driving.
  
  Fig 3: Back-Up Control (Engine Brake) - Line Pressure Characteristic Pattern
  Courtesy of KIA MOTORS AMERICA, INC.
- During shift change
  Set to line pressure that is necessary for shift change. Therefore, line pressure characteristic is set according to input torque and shift types.
  
  Fig 4: During Shift Change - Line Pressure Characteristic Pattern
  Courtesy of KIA MOTORS AMERICA, INC.
- 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: Low Fluid Temperature - Line Pressure Characteristic Pattern
  Courtesy of KIA MOTORS AMERICA, INC.

Shift control

The clutch pressure control solenoid is controlled by the signals from the switches and sensors. Thus the clutch pressure is adjusted to be appropriate to the engine load state and vehicle driving state. It becomes possible to finely control the clutch hydraulic pressure with high precision and a smoother shift change characteristic is attained.