Subaru XT 1988 Service Manual page 566

3-2
AUTOMATIC TRANSMISSION AND DIFFERENTIAL
®
Shifting control (Line-pressure control)
ing operating conditions.
Oil pressure which engages shift clutches (to provide 1st
through 4th speeds) is electronically controlled to meet vary-
In other words, line pressure decreases to match the selected
shift position, minimizing shifting shock.
Fig.
72
_ Line pressure (Clutch operating pressure)
I
Shift clutches
I
ro e pressure
o
Pilot pressure
~ Th
ttl
m
Accumulator control pressure
a
s
1 (
Signal pressure to
control line pressure)
nd shift valve
witching
Transie
to oper
nt oil pressure
t
( Shift select valve)
(
Manual shift valve)
operated through
select lever
Li ne pressure
0
regu I ated for cI
ate cI utches
r
Shift valve
I
I
Manual valve
ptimally t
utch operation
Accumulator
t
Accumulator control
Solenoids 1 and 2
~
pressure
F~~(
I
~
I
Accumulator control valve
I
Drain
r--------
I Duty solenoid A
--,
I
,
r-
------- --------
f-----------
--J.' U .....,i) _
I
,
I
Pressure regulator valve
l~
·t
..
Throttle pressure (also
serves as a signal to optimally
Line pressure
regulate line pressure under
~ .~
built up by
t
varying operating conditions)
oil pump
Drain
8.
0
I
t
Pilot pressure
t
~;f;"
'0
'0
(
)
c
Oil pump Pilot pressure
'"
~
.-
r-
Suction
t
I
Control unit
[)
,
(
Oil tank
Throttle positi
I
, l i o n "
I I L ______________________ - - - - - - - - - - .., accelerator pedal I
\ \.\ I depressing speed, I
, I
I
)._~
I etc. I
I ,
I
I
L _______
.J
L3-933
• Electronic control of clutch oil pressure in summary (5) Fail-safe Function N
a. Solenoids activate through the control unit which receives
various control signals (throttle signal, etc.)
b. Control signals are converted into throttle pressure, which
is transmitted to the pressure regulator valve.
c. The pressure regulator valve optimally regulates line pres-
sure (built-up by oil pump) in response to throttle pressure,
matching varying operating conditions.
52
A fail-safe function is provided to maintain driveability even
if trouble should occur in the vehicle revolution sensor,
throttle sensor, inhibitor switch, or any of the solenoids.
CD
Vehicle revolution sensor
A dual speed-sensing system is used. The speed signal is taken
from the transmission (output shaft revolution sensor) and
also from a sensor built into the speedometer. Even if one
sensor system fails, the vehicle can be controlled normally
with the other sensor system.
®
Throttle sensor
If throttle sensor becomes faulty, throttle will be set to the
predetermined position. (In all ranges, throttle is set to the 5/8
position.)