Subaru XT 1988 Service Manual page 855

STEERING SYSTEM
4-3
Construction
1) Steering sensor
This sensor receives a pulse signal corresponding to the steering
operation. It is constructed with a slit plate placed between
the photo couplers. The slit plate rotates as a unit with the
column shaft. The sensor is located at the bottom of the
column shaft, on the inside of the toe-board.
Column pipe
/ Column ,haft
Sensor plate
/
Photo couplers
L4-1404
Fig. 8
2) Motor pump ASSY
The motor pump ASSY is located on the duct COMPL. in the
engine compartment. An electrical motor rotates the oil pump
in place of the engine-drive unit. With this motor ASSY, high
viscosity steering fluid is quickly warmed in cold weather
below -20°C (_4°F) immediately after the engine starts. As a
result, proper steering performance is maintained.
Fig. 9
I
Electrical motor
Heater
Cap
Strainer
II--IN
L4-1405
9
3) Power controller
This controller regulates current flow to the motor pump
ASSY in response to instructions emitted by the signal con-
troller. It is located by the motor pump on the duct COMPL.
in the engine compartment.
It is equipped with a current sensor, which monitors current
flow through the power controller, a unit which prevents
reception of external noise (radio noise, etc.), and a power
transistor to control current flow.
Power controller
L4-1406
Fig. 10
4) Signal controller
This controller contains a 4-bit microcomputer. It is located
between the rear quarter inner panel and the inner trim. It
receives signals from the car-speed sensor to detect both car
speed and steering operation and controls the operation of the
motor pump ASSY. Since it is a car-speed-sensitive unit, it
serves to reduce steering "assist" as speed increases. It also has
an automatic selective function for high-speed operation,
suburban driving, winding-road driving, and city-driving
modes.
L4-1407
Fig. 11