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7-4
GROUP
7- AUTOMATIC TRANSMISSION
The internally toothed plates are
faced on each side with friction
material and are interchangeable
between the front and rear clutches.
The externally toothed plates, how-
ever, are not interchangeable as the
rear plates are dished. The dished
plate<> can be readily identified as
some of the teeth are omitted.
These plates must always be fitted
with the dishing in the same direc-
tion.
Brake Bands.
Elements of the gear set are held
stationary, to effect an output shaft
speed reduction, by two brake
bands, each operated by a hydraulic
servo. The rear band holds the
pinion carrier stationary to provide
the first gear ratio with engine brak-
ing in Jock-up. The reverse sun gear
is held stationary by the front band
to provide the second gear ratio.
One-way Clutch.
In drive a one-way sprag-type
clutch is used, instead of the rear
band employed in lock-up, to pre-
vent anti-clockwise rotation ot the
pinion carrier.
This one- way clutch allows the
gear set to freewheel when in first
and assists smooth changes between
first and second and vice-versa.
INHIBITOR SWITCH
A non-adjustable inhibitor switch
is mounted on the left hand side of
the transmission.
It is operated by a rod mounted
internally and connected to the
parking pawl.
Four terminals are provided-two
for ignition and two for reversing
lamp connections.
CONTROL SYSTEM
The control system regulates
pump pressure and directs fluid
to the converter and lubrication
system
.
Also, it directs fluid to
the appropriate clutch and servo
pistons, but at a pressure which
varies with vehicle speed and en-
gine
torque.
Three types of valves
are used, regulating valves, shuttle
valves and a manual valve.
Regulating valves operate in
equilibrium which means that the
total force operating in one direc-
tion on the valve is opposed by
an equal and opposite force. These
forces
are
respectively,
spring
forces and
hydraulic
pressures
operating on given areas of the
valves.
Regulated pressures are
controlled by the valves oscillat-
ing between a feed and an exhaust
port to maintain this
equilibrium.
Shuttle valves move in both
directions a fixed distance.
This
movement is caused by the forces
in one direction exceeding the
forces in the opposite direction.
These forces are respectively spring
and hydraulic pressure acting upon
given areas of the valves. These
valves are used to direct or to pro-
vide an exhaust for fluid.
The manual valve
is
controlled by
the position of the selector lever and
directs fluid, or provides an exhaust
from, the clutch and servo pistons
according to the position selected.
OIL PUMP
The oil pump driven by the
torque converter impeller, oper-
ates whenever the engine is run-
ning.
All the hydraulic require-
ments of the torque converter and
automatic transmission are sup-
plied by this pump.
The oil pump consists of an inner
externally toothed gear in mesh with
an internally toothed gear housed
eccentrically to the inner gear. The
drive to the pump inner gear is by
tangs on the drive shaft attached to
the torque converter and the gear
revolves about the torque converter
support on the pump adaptor plate.
The operation of the oil pump is
shown diagrammatically in
Fig. 5.
As the gears revolve, oil is drawn
from the sump through the inlet port
into the space between the gear teeth
as they come out of mesh and is
carried round between the gear teeth
to the
outlet-
port where the teeth
again mesh.
The oil is forced out through the
outlet port and flows to the regulator
valves which control the delivery
pressure.
PRIMARY REGULATOR VALVE
This valve regulates pump pres-
sure. Control pressure, operating
on a small area of the valve, is
affected by modulated throttle pres-
sure operating on one end of the
valve. These forces are opposed by
the primary regulator valve spring
and
~hrottle
pressure acting on the
opposite end of the valve. The con-
trol pressure produced varies with
the accelerator pedal position and
car speed, and provides the correct
clutch and servo capacity under
operating conditions.
This control pressure is directed
to the manual valve and throttle
valve from the primary valve.
SECONDARY REGULATOR VALVE
This valve controls convertor
and lubrication pressures. Conver-
tor pressure acting on one end of
the valve is opposed by spring
force on the other end.
GOVERNOR
The governor, mounted on and
rotated by the output shaft, is a
pressure regulating valve which
reduc<:s control pressure to a figure
that varies with the output shaft,
speed, and therefore, car speed.
This variable pressure in the
control system effects up and down
changes through the first to second
and second to third shift
valves.
When the governor rotates at low
speeds
(Fig.6), the governor weight
and valve move outward by centri-
fugal force. This outward force is
opposed by hydraulic pressure pro-
duced by governor pressure acting
upon a small area of the governor
valve. Since the governor valve
is a regulating valve, and attempts
to remain in equilibrium governor
pressure will rise in accordance
with the increase in centrifugal
force caused by increased speed of
rotation.
As output shaft speed increases,
the governor weight moves out-
wards to a stop in the governor
body. When this happens, a spring
located between the weight and
the governor valve becomes ef-
fective. The constant force of this
spring combines with the governor
valve centrifugal force to oppose
governor pressure, so rendering
governor pressure less sensitive to
output shaft speed variations.
Manual Centro! Valve.
This valve, actuated by the selector
lever directs control pressure to, or
exhausts fluid from, the appropriate
valves or modulator valve and plun-
ger components, according to the
position selected.
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