Automatic
Transmission
HYDRAULIC
CONTROL
UNIT
AND
VALVES
The
hydraulic
or
a
tomatic
control
system
is
comprised
of
four
4
basic
groups
the
pressure
supply
system
the
pressure
regulating
system
the
flow
control
valves
and
the
friction
elements
PRESSURE
SUPPLY
SYSTEM
The
pressure
supply
system
consists
of
a
gear
type
oil
pwnp
driven
by
the
engine
through
the
torque
converter
The
pump
provides
pressure
for
aU
hydraulic
and
lubrication
needs
PRESSURE
REGULATOR
VALVES
The
pressure
regulating
valves
con
trol
the
output
pressure
of
the
oil
pump
Pre
ure
rellulator
valve
The
pressure
regulator
valve
con
trois
mainline
pressure
based
on
throttle
opening
for
the
operation
of
the
band
clutches
and
brake
Governor
valve
The
governor
valve
transmits
re
gulated
pressure
based
on
car
peed
to
the
shift
valves
to
control
upshifts
and
downshifts
Vacuum
throttle
valve
The
vacuum
throttle
valve
transmits
regulated
pressure
based
on
engine
load
vacuum
This
pressure
controls
the
pressure
regulator
valve
Also
this
pressure
is
applied
to
one
end
of
the
shift
valves
in
opposition
to
governor
pressure
which
acts
on
the
other
end
of
the
shift
valves
controlling
upshift
and
downshift
speeds
FLOW
CONTROL
VALVES
Manual
valve
The
manual
valve
is
moved
manual
Iy
by
the
car
operator
to
select
the
different
drive
ranges
1
2
ShHt
valve
The
1
2
shift
valve
automaticaIly
shifts
the
transmission
from
first
to
second
or
from
second
to
first
depend
ing
upon
governor
and
throttle
pres
sure
along
with
accelerator
position
solenoid
downshift
valve
See
Hy
draulic
Control
Circuits
Drive
2
2
3
ShHt
valve
The
2
3
shift
valve
automaticaIly
shifts
the
transmission
from
second
to
top
gear
or
from
top
to
second
de
pending
upon
governor
and
throttle
pressure
or
accelerator
position
sole
noid
downshift
valve
See
Hydraulic
Control
Circuits
Drive
3
Range
2
3
Tlmlnll
valve
For
2
3
shifts
a
restrictive
orifice
slows
the
application
fluid
to
the
front
clutch
while
the
slower
reacting
band
is
allowed
to
release
This
prevents
a
hard
2
3
or
3
2
shift
Under
heavy
load
however
the
engine
will
tend
to
run
away
during
the
2
3
or
3
2
shift
pause
therefore
a
2
3
timing
valve
using
throttle
and
governor
pressure
is
used
to
bypass
the
restrictive
orifice
during
such
heavy
load
conditions
Solenoid
down
hHt
valve
The
solenoid
downshift
valve
is
activated
electrically
when
the
ac
celerator
is
f1oor
d
causing
a
forced
downshift
from
top
to
second
top
to
first
or
second
to
first
gear
depending
upon
car
speed
governor
pressure
AT
3
Pre
ure
modified
valve
The
pressure
modifier
valve
assists
the
mainline
pressure
regulator
valve
in
lowering
mainline
pressure
during
high
speed
light
load
conditions
such
as
steady
speed
cruise
Governor
pres
sure
working
against
a
spring
opens
the
valve
which
aUows
modified
throt
tle
pressure
to
work
against
the
pres
sure
regulator
valve
spring
lowering
mainline
pressure
Lower
operating
pressure
under
light
load
reduces
oil
temperature
and
increases
transmis
sian
life
Throttle
back
up
valve
The
throttle
back
up
valve
assists
the
vacuum
throttle
valve
to
increase
line
pressure
when
the
manual
valve
is
shifted
either
to
2
or
I
range
Second
lock
valve
The
second
lock
valve
is
used
to
bypa
the
1
2
shift
valve
to
maintain
the
band
apply
pressure
in
2
posi
tion
The
valve
is
also
used
as
an
oil
passage
for
the
1
2
shift
valve
band
apply
pressure
in
D2
D3
and
12
Range
CLUTCHES
AND
BAND
SERVOS
The
servo
pistons
of
the
clutches
low
reverse
brake
and
band
are
moved
hydraulically
to
engage
the
clutches
brake
and
apply
the
band
The
clutch
and
brake
istons
are
released
by
spring
tension
and
band
piston
is
released
by
spring
tension
and
hy
draulic
pressure
