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 1: Normal Time Line Pressure Characteristic Graph
  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 2: Line Pressure Characteristic For Backup Control Graph
  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 3: Line Pressure Characteristic During Shift
  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 4: Line Pressure Character During Low Temperature
  Courtesy of KIA MOTORS AMERICA, INC.