Subaru 2002 Impreza Service Manual page 249

TRANSMISSION CONTROL MODULE (TCM)
Automatic Transmission
L: AWD CENTER DIFFERENTIAL CONTROL (TURBO MODEL)
1. CONTROL DESCRIPTION
The TCM controls the engagement of the center differential's multi-plate clutch (LSD) using maps
that are pre-programmed based on the throttle opening and engine speed. It selects a map ac-
cording to driving conditions and use it as the control basis.
2. ORDINARY CONTROL
A specific map is given to each of the 1st to 4th gears and the reverse gear for use by the TCM
to control the torque distribution appropriately during ordinary driving conditions.
The maps are programmed in such a way that the differential action limiting torque decreases as
the throttle valve opening decreases and as the vehicle speed increases. This way of control is
employed in order to reduce internal circulation of torque and also to improve steering perfor-
mance and stability of the vehicle's behavior when the accelerator pedal is released or when a
downshift is performed, thus upgrading the stability achieved by the AWD system.
3. START CONTROL
When the vehicle speed is 0 km/h (0 MPH), the TCM makes control to generate differential action
This enables the vehicle to start smoothly without swerving even on a slippery road.
,.limiting torque that is proportional to the throttle angle.
4. TURNING CONTROL
The TCM makes a correction such that the input torque to the multi-plate clutch
steering angle increases.
This function is performed to improves turning performance at certain vehicle
5. SLIP CONTROL
is reduced as the
speed range.
When front or rear wheels start slipping with the vehicle running slower than the predetermined
speed, the TCM makes control to increase the differential action limiting torque.
This function maintains traction and improves driving stability.
T
Low- Vehicle speed
+
High
NF0489
AT-27