Neutral
Clutches A, B, C, C and D are disengaged.
All pinions in the planetary gear set (1) can turn
freely on their shafts.

1. Gear
Clutch A is engaged. On traction the planetary gear car-
rier bears against freewheel 3; on the overrun it turns
freely on the freewhell.
With the selector lever at 1 or 2 clutch D is also engaged
in 1. gear in order to be able to brake with the engine.

2. Gear
Clutches A, C and C´are engaged.
Freewheel 3 is overrun. The hollow shaft is blocked with
freewheel 2. This locks the two sun gears.

3. Gear
Clutches A, B and C´are engaged. Freewheels 2 and 3 are
overrun. The entire planetary gear set turns as a unit at a
ratio of 1 : 1.

Reverse gear
Clutches B and D are engaged. The direction of rotation
of the drive pinion is reversed by locking the planetary
gear carrier.

The 3-HP-20 is a fully automatic transmission. It is fitted
with a torque converter and a Simpson planetary gear
train.
P Parking
R Reverse
O Neutral
A 1., 2. and 3. gear
2 1. and 2. gear (3. gear locked)
1 1. gear (2. and 3. gears locked)
With the selector lever at P the transmission drive pinion
is locked mechanically by a pawl.
R - Reverse gear.
With the selector lever at O or P the engine can be
started. In these positions there is no power transmitted to
the rear wheels.
The selector lever is set at A for normal driving conditions
to guarantee favourable fuel consumption figures.
The kickdown can be applied to have the transmission
downshift earlier than usual.
The selector lever is set at 2 when driving in hilly or
mountainous regions to save the transmission from con-
tinuously shifting between 2. and 3. gears. The engine
braking effect is also better.
Driving range 1 is provided for constant engine braking
effects in mountainous regions.
Driving ranges 1 or 2 can be selected at any road speed.
It will only mean that the transmission will no longer shift
up to the next higher gear.

The torque converter operates as a fluid coupling and a
torque booster. The impeller P turns at engine speed and
shovels the oil clockwise into the turbine wheel (T). When
a range is engaged the turbine wheel and drive shaft are
connected with the planetary gears via the clutches. As the
engine speed increases the oil is thrown counterclockwise
out of the turbine wheel (due to the shape of the turbine
wheel vanes) into the rotor (L) turning in opposite direc-
tion to the engine and thus is fed back to the impeller
with a minimum of disturbance. The back pressure caused
by changing the direction of flow produces an increase
in torque. The largest increase in torque is produced when
on a stationary car the impeller driven at full throttle has
to drive the stopped turbine wheel.
As the road speed increases, the difference in speed of
rotation between the impeller and turbine wheels falls
until the so-called locking point is reached at a ratio of
1 : 1. As this point the rotor ceases to be locked against
the freewheel and begins to run forward in the oil flow
between the impeller and turbine wheels. As the road
speed increases still further, and the vehicle begins to
overrun and attempts to turn the engine, the torque con-
verter functions as a straight-forward fluid coupling. On
the overrun this means that the braking effect of the
engine can be partially exploited.

The primary pump is driven from the torque converter at
engine speed. Its function is to supply oil to the converter,
the control unit and the clutches.
Key to hydraulic control circuit diagram
The main pressure valve determines the pressure level in
the control unit. As soon as the control unit is filled with
oil, the oil supply passage to the converter is opened.
As the flow rate increases, excess oil is returned to the
intake passage of the primary pump.
The converter pressure valve prevents excess from
building up in the converter.
The selector slide valve is operated mechanically from
the selector lever. It directs the oil pressure in the control
unit to the appropriate circuits for the desired gear rations.
The throttle pressure valve is connected to the throttle
cable and it determines the shift points with the regulator,
depending on the position of the throttle valves.
The shut-off valves initiate downshifts through the gears
independently of the throttle valve position. In addition
the shut-off valves prevent further automatic gear shifts
when the selector lever is in position 1 or 2.
The selector valves determines the gear selected. A soon
as spring pressure in the selector valve is overcome by
regulator pressure, the oil supply can reach the clutch
valves and engage the relevant clutches. When the kick-
down mechanism is operated, spring pressure is reinforced
by throttle pressure. This means that the engine must reach
a higher speed before the regulator pressure can over-
come the combined spring and throttle pressure.
The clutch valves and dampers are intended to make gear
shifts as smooth as possible.
The regulator determines the shift points with the shift
valves in accordance with throttle valve pressure. The
regulator pressure is developed in proportion to drive
pinion speed of rotation.
From the selector slide valve the oil flows to passage (1).
When accelerating, piston (A), regulator bush (B), spring
(C) and slotted disc (DI are moved outwards by centrifugal
force, until the upper control surface of the regulator
piston passes passage (1) and allows the oil to flow into
passage (2). As a result of the tapering surface (Y) on the
regulator piston, pressure in passage (2) is for a brief
period higher than the centrifugal force of the piston. This
presses back the regulator bush and the lower control
edge frees lead passage (3) for a time, unit the pressure
in passage (2) is balanced against the load exerted by the
components subjected to centrifugal force. At this point
the pressure in passage (2) is the so-called regulated pres-
sure dependent on engine speed, and the regulator bush
tends to oscillate between passage (1) and (3).