SKODA Self Study Program 20 – Automatic Gearbox – Fundamentals SSP-20-Automatic-gearbox-fundamentals

Automatic Gearbox

- Fundamentals -

The gearbox in a motorcar is the technical aid for
converting the engine forces into the varying
operating conditions.

Operating the clutch and shifting gears make up
the lion’s share of the physical effort involved in
driving a motor vehicle.
The purpose in using „self-shifting gearboxes“ is to
considerably reduce this physical effort, enhance active
safety so that the driver’s responsiveness is directed fully
to the traffic situation.

SP20-3

The progress in electronics makes it possible to interlink electronic functional details

and hydraulic systems and to achieve safe „automatic“ driving with a high level of effi­ciency. That is why automatic gearboxes feature increasingly as part of the equipment
available in modern motor vehicles.

The operating principle of an automatic gearbox is basically the same in all passenger
cars. They vary in design details depending on how they are installed and on the power
output of the engine.

This self study programme is intended to impart to you the basic design of an automatic
gearbox and the operation of certain components. The components presented apply
in the vast majority of cases to all automatic gearboxes or are identical to those used
in gearbox 01M fitted to the OCTAVIA.

2

Contents

Power Conversion 4

General Design 7

Determining Shift Point 9

Automatic Transmission Fluid 14

Torque Converter 16

Lock-up Clutch 18

Planetary Gear Systems 19

Shift Elements 23

Multi-disc clutch
Multi-disc brakes
Band brakes
Freewheel

Gearbox Control 27

System overview of an automatic gearbox
Emergency programme/Self-diagnosis

Hydraulic System 31

Hydraulic fluid circuit/hydraulic fluid pump
Hydraulic shift control unit
Diagram of hydraulic system
Pressures in the hydraulic system
Hydraulic shift elements

Test Your Knowledge 38

23
24
24
26

28
30

31
32
33
34
36

You can find specific information on the
automatic gearbox 01M fitted to the SKODA
OCTAVIA in the Self Study Programme Booklet

21.

3

Power Conversion

Why convert the power?

Let’s recall a number of basic rules of automotive
engineering.

The power for driving a motor vehicle and the neces­sary ancillaries (e.g. power-assisted steering, air con­ditioning compressor) is produced by the engine.

The power P is the mathematical product of torque M
multiplied by the speed n divided by the numerical
factor 9550*.
The unit of measure is kW.

The power increases with engine speed and torque.
What does the term torque tell us?

Torque describes the power transmission through a
shaft or gear.
It is designated with the formula character M and is
formed from the force F which acts on the circumfer­ence of the rotating part, multiplied by its radius r.
The term which describes the engine speed is the
angular velocity ω in 1/s.
The unit of measure of torque is Nm = Newton meter.
In the case of the gearbox it is the gears which pos­sess a certain lever arm „r“.

Internal combustion engines can, however, only be
operated between idling speed (in the case of a car
approx. 600 to 700 rpm) and maximum speed (which

differs according to engine design, on average 6000
to 7000 rpm).
In contrast, maximum torque is achieved only within a
narrow engine speed range.
It rises to its maximum value and drops off again
within the range of rated engine speed.

That is why we need to have a torque converter in a
vehicle for adapting this limited engine speed range
to the wide range of the tractive force required.
This torque converter is the gearbox.
In theory, a gearbox with an infinite variety of steps
would be required for adapting to tractive force
demand.
This is not a practical concept.
That is why we attempt to approach the ideal pattern
of a tractive force curve by using several constant
steps = engageable ratios.

* The numerical factor 9550 results from the conversion of all

mathematical quantities when the numerical values for n and M
are entered in the equation with rpm and Nm, respectively. This
produces the result P in kW.

M • n

P =

9550

Power-torque diagram of a petrol engine

M = F • r

ω

I

(N)

II

Tractive force at driven

wheels

Tractive force - vehicle speed diagram

ideal tractive force curve
Tractive force curve of gear I to IV

n = 5000 rpm

●

III

IV

v (km/h)

o

r

n = 1000 rpm

SP20-6

F

M

SP20-45

SP20-8

4

The manual gearbox

When it comes to a gearbox, therefore, we can refer
to it as a device for converting torques.
Speed n and torque M behave in this case in the
reverse ratio, in other words a torque which flows in at
the input of the gearbox appears again intensified at
the gearbox output.
The torque gain is obtained, however, by a loss in
rotational speed.
The engine power is not altered as a result of the
gearbox.

n

n

A manually-shifted gearbox is generally designed as
a countershaft gearbox.
We are familiar with this from all SKODA models.

The power in this case flows from the input shaft
through a fixed gear combination to the main shaft
and on to the final drive.

The sliding gears on the main shaft run loose and it is
only once a gearshift is performed that they are cou­pled to the shaft by means of sliding sleeves.

Manual gearboxes therefore operate on a positive
locking basis - in contrast to automatic gearboxes
which operate on a non-positive basis.

The torques vary as a function of the transmission
ratio „i“.

i =

n
n

Speed of driving gear

1

=

Speed of driven gear

2

SP20-7

M

Output

= M

Important:
When starting off and shifting gears in a car fitted with a manual gearbox,
the power flow from the engine to the gearbox has to be interrupted.
As you know, it is not possible to shift gears when the engine is operating
under load.
This requires a special mechanical device - the clutch.
When engaged, the clutch transmits the engine torque to the gearbox and
the driven wheels and, when disengaged, it interrupts the power flow.

Input

• i

SP18-22

5

Power Conversion

Today's manual gearboxes do admittedly reflect the state of the art ...........

There has been a considerable improvement in the operation of manual gearboxes in recent years:

– gearshifting simplified by means of synchromesh
– quiet gearshifting as a result of helical gears
– transmission ratios adapted to engine output and tractive force demands optimally

matched between the gears

– designing car gearboxes which for the most part offer 5 gears.

Clutches, too, have also undergone numerous improvements, in particular in respect of reducing the
pedal forces required.

How a clutch and gearbox for modern cars are designed and operate is described in
Self Study Programme 18.

But ............

If a car is driven a distance of 10,000 km - as test runs have revealed - the clutch pedal is moved
about 30,000 to 40,000 times.

And the gears are shifted manually with the gearshift lever just as often.
It's therefore no surprise at all that opinions vary considerably when it comes to a manual gearbox.

SHIFTING GEARS IS FUN

- IS THE ONE OPINION

SP20-13

SHIFTING GEARS IS HARD WORK

that is why, have the work done for your

SP20-14

Nevertheless, there were a great many prejudices to overcome in the course of developing automatic
gearboxes.
They were considered as "weak" and "not sporty".

- IS THE OTHER OPINION

automatic gearbox!

Nowadays, thanks to computer technology in the car with electronic shift programmes and determina­tion of the shift point using fuzzy logic, such arguments no longer hold true.

6

General Design

The differences
What are the differences between a car fitted with a manual gearbox and a car fitted with an

automatic gearbox?

The power flow in both cars is the same

Engine - Clutch - Gearbox - Differential - Drive Shafts - Running Gear

with automatic gearboxwith manual gearbox

Mechanical clutch, operated manually

Manual gearbox with countershaft

with positive-locking gearshift

Driver involved in shifting gears.
Eyes and ears sense the driving situation.

The power flow is interrupted during a gearshift.
As a rule, the car moves without power for 1 to 2
seconds during a gearshift (depends on driver).

mechanism (using gearshift
lever, shift fork, sliding sleeve)
for transmitting the torque

SP15-19

SP15-18

Torque converter automatically separates the
rotating engine from the stationary gearbox when
the car is not moving, but also performs addi­tional tasks and can be regarded as a hydraulic
gearbox.

Planetary gear

Is an essential requirement for at
all making use of automatic con­trol, automatic non-positive
torque transmission through
clutches and brakes.

More relaxed driving, sensors detect the driving
resistances. Electronic gearbox control proc­esses information for selecting a gear which is
engaged by hydraulic shift elements.

Automatic gearboxes operate without any inter­ruption to the power flow and therefore acceler­ate continuously.
When it comes to acceleration performance, they
are the equal of a manual gearbox.

Increased physical demand on the driver, full
concentration on driving situations.

Driving comfort is enhanced, stress is reduced,
overall safety is improved.

7

General Design

Automatic gearboxes therefore perform the tasks of

– starting off
– selecting the transmission ratio
– engaging the selected gear automatically.

The only element which is involved in starting off is a hydrodynamic torque
converter

Automatic gearbox

- Main components -

hydraulic pressure-operated multi-disc clutches and brakes

(assigned to the individual elements of the planetary gear train)

Torque converter

For starting off, for increasing torque and

minimizing vibrations

Planetary gear

For mechanically forming the ratios/gears

Shift elements

for carrying out the gear change

Freewheels

For optimizing the engagement of load with

the shift elements

Gearbox control

(electronic/hydraulic) based on shift programmes

Oil pump

For supplying the shift elements, the torque converter

and for lubricating the gearbox

8

Determining Shift Point

When it comes to carrying out the automatic gearshifts, in other words converting the torque in line with
the driving situations which exist, what is of interest in addition to the purely mechanical gearbox design
(planetary gear), are the following three questions.

1. How does the automatic gearbox control detect adaptive shift curve
when a gearshift should be made?

2. Who supplies this information to the control unit? sensors

3. How are the gearshifts effected? hydraulically by means of

actuators/solenoid valves

Let's look in this connection at the system functions for an automatic gearbox, as exist also in the
SKODA OCTAVIA.

Sensors

Accelerator pedal
position

Vehicle speed

Gearbox speed

Engine speed

ATF temperature

Selector lever position

Brake pedal operation

Kickdown switch

Actuators

Gear selection
valve

Torque converter
lock-up valve

Main pressure valve

Selector lever lock

Control

unit

Engine torque reduction

Starter lockout

Idle speed increase

Self-diagnosis

Air conditioning

Selector lever display

The shift logic is computed through digitally by a microprocessor in the control unit.
The electronic gearbox control constantly repeats the detection of the sensor signals, calculates the
shift decision and transmits it to the actuators. This cycle is completed in 20 ms.

9

Determining Shift Point

Conventional shift characteristic line

Shifting between two gears is carried out by
the electronic gearbox control on the basis
of a shift characteristic line. This takes into
account vehicle speed and accelerator
pedal position.
A different characteristic line applies to
upshifts than to downshifts.
A shift characteristic line is stored in the
control unit for each gear change as a func­tion of vehicle speed and accelerator pedal
position.

Upshift
Downshift

3 – 4

This selection of shift points is relatively
rigid as gearshifts are always made at the
same points in line with the position of
accelerator pedal and the speed of the car.
The diagram illustrates only the 3rd - 4th
gearshift.

Sport characteristic line
ECO characteristic line

During the initial period of electronic gear­box controls, therefore, only fixed shift char­acteristics were programmed.

As the electronic gearbox control under­went further development, it was possible to

select between two programmes:

- a sporty

- and an economic programme

A separate switch on the selector lever pro­vided the

selecting

tics. A subsequent development was to
automate this switchover.
This was done by sensing the rate at which
the accelerator pedal was depressed. Nev­ertheless, as with the previous system, this
was also an absolute decision

driver

with the possibility of

one or the other shift characteris-

"ECO" or "SPORT"

Vehicle speed

Vehicle speed

Position of accelerator pedal

Sport

ECO

Position of accelerator pedal

4 – 3

SSP172/116

3 – 4
3 – 4
4 – 3

4 – 3

SSP172/117

10

Adaptive characteristics

Modern electronic gearbox controls - as is also the case for the
01M gearbox in the SKODA OCTAVIA, calculate a shift in the
characteristic line from a large variety of information which con­stantly describes the current operating and driving situation.

This individually adapted, non-rigid shift characteristic is used in
the control unit for the shift decision.
We talk in this connection of an adaptive shift characteristic.

The

driving resistance-based shift programme

recognizes driving resistances such as climbing or
descending a hill, towing a trailer and driving into the wind.
The control unit calculates the driving resistance on the basis of the speed of the car, the position of the
throttle valve, the engine speed and the acceleration of the car, and uses this as a basis for specifying the
shift points.

The calculation of the gearshift point based on the driver's style and driving situation is conducted using the fuzzy
logic principle

1

0

Sporty factor

%

90
80
70
60

50
40
30

20
10

ECO

0

Accelerator pedal speed

100 %

Sporty factor

Sport

SP20-11

With the speed at which the driver operates the accelerator pedal,
he produces a sporty factor which is determined by the fuzzy logic.
This sporty factor is used to determine a floating gearshift point
between a shift point design oriented more to good fuel economy
or more toward performance.
It is thus possible to have any number of shift points between the
"ECO" and the "SPORT" shift characteristic.
It is thus possible to react much more responsively to the individual
driver's wishes.

11

Determining Shift Point

What does fuzzy logic mean?

Fuzzy logic is something which we encounter today
in a large number of items of equipment which are
part of our daily life.
Washing machines, vacuum cleaners, video cam­eras or electric razors nowadays are controlled by
fuzzy logic.

The word fuzzy in this connection means more or
less a "specifically applied out-of-focus".

SP20-46

What we do when we make use of fuzzy logic is to
eliminate the classical hard shift states for a rigid
classification does not permit any tolerance in
assigning quantities.

Classical division
The example below is intended to illustrate to you

the classical rigid allocation of quantities in a compu­ter without fuzzy logic:
If a computer has to distinguish between hot and
cold, it is then necessary to provide it with a fixed
limit (in this example 80°C).

hot

1

cold

0

0 °C

Temperature

80 °C

The computer is able to distinguish between hot and
cold on the basis of the switching states.
This rigid classification does not allow the computer
any tolerance in allocating quantities.

Switching states

1

Switch
closed

or

0

Switch

open

Yes

No

12

SSP172/107

It is often necessary to take decisions which come somewhere between these rigid statements of "hot"
and "cold".

Fuzzy logic makes allowance for an intentional out-of-focus (fuzziness) which does not operate with two
values but with result quantities.

What we then have is an infinite variety of intermediate values such as "almost cold", "cool", "lukewarm"
or "too warm".

hot 1

almost hot
too warm

warm

lukewarm
cool

almost cold
cold 0

The upper limit of "hot" and the lower limit of "cold", as well as all the intermediate levels,
are assigned to precise temperatures.

10

20

30

5040

60

The size of the areas produced by the intersections -

cold

blue area relative to red area - enables the fuzzy logic
to recognize how these different temperature levels
are assigned to the previously precisely specified inter­mediate values.

70

80 °C

80 °C

SP20-10

lukewarm

hot

°C

19

SP20-9

Consequently, at 19°C,
88% of the entire area is assigned to blue = cold and
12% of the entire area is assigned to red = hot.

The fuzzy logic recognizes "lukewarm".

13

Automatic Transmission Fluid

Automatic Transmission Fluid = ATF (Automatik Transmission Fluid)

The fluid in the automatic transmission has to satisfy varying
demands as it circulates.

It has to

– Transmit forces (in torque converter)
– Perform shift movements (in the hydraulic shift elements)
– Produce friction (in the multi-disc clutches and brakes, in the

lock-up clutch)
– Lubricate parts (all rotating gearbox parts)
– Dissipate heat
– Remove abrasion.

The automatic transmission fluid has to perform these tasks within a
temperature range from -30°C up to 150°C (temperature measuring
points in the oil pan of the gearbox).

Temperatures of up to 250°C to 400°C may occur for short times
during a gearshift at the multi-disc clutches and brakes.

SP20-4

That is why the mineral base oil for automatic gearboxes is provided
with a number of additives to enable and to perform all these tasks
no matter the conditions which exist. In particular, the viscosity
index is improved in order to ensure uniform viscosity over the entire
temperature range.
Standards which have been compiled for this purpose by General
Motors (ATF Dexron) and Ford (ATF Mercon) are recognized world­wide.

Note:
Use only the automatic transmission fluid ap­proved by the vehicle manufacturer.
Other fluids or additives result in changes to the
properties and have a detrimental effect on the
operation and life of the gearbox.
In particular, water elements in the automatic
transmission fluid can cause operational prob­lems.
The ATF is kept clean by passing it through a fil­ter as it flows out of the oil pan.
A strong permanent magnet in the oil pan traps
any metallic abrasion.

Additive

SP20-5

14

ATF level/ATF temperature

ATF level and ATF temperature have a
major influence on proper operation of an
automatic gearbox.

Too high Too low

ATF tempera-

ture too high

Gearshifts take too

long

ATF foams

ATF flows out of

breather

That is why automatic gearboxes feature a
temperature sensor which measures the
ATF temperature, and also an ATF cooler.
The block diagram below illustrates the
interrelationships.

ATF level

Clutches/brakes close too

slowly

Gearshifts performed with

time lag

Operational problems in

gearbox

Even if the temperature is exceeded by a
small amount this can result in changes to
the ATF level. The expansion of the ATF
takes place not in the oil passages but
occurs in the oil pan.
In particular, the heating up of the ATF in
the torque converter forces it into the oil
pan.

An excessive ATF level results in foaming
and in ATF flowing out of the overflow.

Important!
Incorrect filling of an automatic gearbox
can result in operational problems and
damage to the gearbox.

Service

Inspect ATF level and

adjust, if necessary

Pay particular attention to the inspection tem­perature of the ATF if adjusting the ATF to
the correct level.

The inspection temperature should be meas­ured with the diagnostic tester and set to the
specified temperature.

When inspecting the ATF level, proceed as
stated in the current Workshop Manual for
the relevant gearbox.

If the quantity of ATF is correct, the electronic
gearbox control automatically compensates
for a change in viscosity as a result of a tem­perature increase by changing the oil pres­sure in order to ensure uniformly smooth
gearshifts.

15

Torque Converter

The hydrodynamic torque converter

The hydrodynamic torque converter is, in fact, an
additional hydrodynamic transmission to the auto­matic gearbox.

It forms the initial element of the automatic gearbox.
The principle of the torque converter was first used

in 1905 by Hermann Föttinger in marine engineer­ing.
That is why the hydrodynamic torque converter is
often referred to as the Föttinger converter.

The principle of the torque converter:
A pump draws in a fluid - in our case the special
automatic transmission fluid - accelerates it and
passes it to a turbine.
The hydrodynamic energy is thus converted into a
mechanical rotating movement.

Impeller

Pump
wheel

Components

Propulsion effect

Turbine
wheel

SP20-15

The torque converter consists of three main parts:

– Pump wheel (this is also the housing of the

torque converter)

– Turbine wheel (which powers the turbine shaft

and thus the gearbox)

– Impeller (connected by a freewheel to the

gearbox housing, it is able to rotate only in the
same direction as the pump wheel and turbine

wheel)
It is filled with a special automatic transmission fluid
and is pressurized.

The pump wheel (at the same time the housing) is
driven by the vehicle engine with a direct speed.
As a result of the centrifugal force the ATF is forced
out between the blades of the pump wheel.
It is deflected toward the turbine wheel at the inner
wall of the housing.
This hydrodynamic energy is absorbed by the
blades of the turbine wheel and it rotates.
The hydrodynamic energy is converted into a
mechanical rotating movement.
The ATF flows back in the vicinity of the shaft of the
torque converter through the vanes of the impeller
positioned relative to the pump wheel.
The internal ATF circuit in the torque converter is
closed.

16

Torque increase

Pump wheel

Turbine
wheel

Freewheel

Impeller

Transmitting energy by means of ATF flow

SP21-31

In the torque conversion phase, the torque con­verter converts the reduction of rotational speed
into an increase in torque.

At the moment the vehicle starts off, only the pump
wheel rotates initially. The turbine is stationary. The
difference in speed - known as slip - is 100 %.
Slip is reduced to the extent that the ATF passes
the hydrodynamic energy to the turbine wheel.
Pump speed and turbine speed move closer
together.

The torque converter slip is the operationally nec­essary criterion for converting the torque.
At a high slip, the torque boost is at its maximum, in
other words if there is a large difference in speed
between pump wheel and turbine wheel, the ATF
flow is deflected by the impeller.
The impeller thus has the effect of boosting torque
in the torque conversion phase.
It is supported by means of a freewheel at the gear­box housing during this operation.
When slip is low, in other words when pump wheel
and turbine wheel are operating at practically the
same speed, the impeller no longer has the effect
of boosting the torque.
In this case, it then rotates in the same direction as
the pump wheel and turbine wheel thanks to the
freewheel. It thus causes scarcely any losses in
efficiency.

The turbine wheel is stationary.

Starting-off
Torque conversion phase 1

Pump wheel is rotating.
ATF flow sharply deflected. High slip.
Gearing down.

Maximum boost in torque.

Turbine speed increases.

Torque conversion
phase 2

ATF flow is "stretched". Slip is reduced,
transmission ratio decreases.

Torque boost decreases.

Turbine speed practically pump speed.

Clutch phase

Low slip, impeller also rotates.
Torque ratio shrinks to 1:1.

Operates only now as clutch.

Hence: The torque converter operates in the slip range as a hydraulic gearbox with a variable

ratio.

17

Lock-up Clutch

Torque converter lock-up clutch - a
mechanical clutch

Lock-up
clutch

Turbine wheel

Torque flow

SP21-34

Why is the torque converter locked up?
Once the clutch phase is reached, in other

words the torque ratio is 1:1, the torque con­verter operates with relatively high losses.
The efficiency as a rule is around 85 %, and may
even be as much as 97 % in the case of high­performance engines which operate at high
speeds.

Two to three percent of slip are always required,
however, for transmitting the power otherwise
the ATF flow would come to a stop.

Losses in transmitting power always, however,
have an impact on economic operation of the
vehicle.
That is why modern automatic gearboxes are
equipped with a lock-up clutch. This locks up the
torque converter, if necessary, if the slip level is
low and takes it out of operation.

The lock-up clutch is integrated in the housing of
the torque converter. It is provided with a ring­shaped friction lining and is connected to the tur­bine wheel. It is pressed by means of oil pres­sure against the torque converter housing which
also serves as the torque input.
This ensures a rigid, slip-free transmission of
power.

In the same way as a normal dry friction clutch,
the torque converter lock-up clutch features tor­sion dampers for reducing engine torsional oscil­lations.
It is the control unit of the automatic gearbox
which determines when the lock-up clutch
closes or opens.

18

Operation

Depending on the characteristics of the vehicle
and gearbox, it is possible in practice to improve
the fuel economy of a car fitted with an auto­matic gearbox by 2 to 8 % by means of a torque
converter lock-up clutch.

Self Study Programme 21 contains further infor­mation on the hydraulic control of a torque con­verter lock-up clutch.

Planetary Gear Systems

The gear change - manual gearbox

The gear change - automatic gearbox

What alternatives are there?

A gear change in the manual gearbox proceeds as
follows, as most of you will be aware:

– Disengage shift sleeve, power flow

interrupted
– Gear is brought to the same speed,
– Then, the selected shift sleeve is engaged

and the power flow is restored

There is no possibility in the case of an automatic
gear change for any interruption to the power flow,
which is what we wish from an automatic gearbox.

The automatic control unit cannot derive from the
traffic situation when it would be the right moment
to interrupt the power flow.

When it comes to an automatic gearbox, it is only
gearboxes which can also be shifted without any
interruption of the power flow, which are suitable.
This is the case for planetary gear systems. That is
why they form the design basis of almost all auto­matic gearboxes.

1

2

3

4

SP20-31

A planetary gear system is composed of two to four
planet gear sets.
These are permanently connected to each other or by
means of clutches.
The operating principle can be explained by taking
one planet gear set.

A planet gear set consists of

– a central gear

the sun wheel - 1 -

– several planet gears (three to six) - 2 ­– the planet carrier - 3 ­– an external internally-toothed

hollow gear - 4 -

All the pairs of gears are constantly meshed.
It is not necessary to have shift sleeves. The gear
speeds do not have to be synchronised.

19

Planetary Gear Systems

The sun wheel -1- rotates in the inside on a cen­tral shaft.
The planet gears -2- mesh with the teeth of the
sun wheel.

SP20-2

1

2

The planet gears are able to rotate both about
their own axis as well as on an orbit around the
sun wheel.

The planet gears are housed together with their
shafts in the planet carrier -3-.
The planet carrier permits the rotational move­ment of the planet gears around the sun wheel
and, logically, also thus around the central shaft.

3

The inner teeth of the hollow gear -4- mesh with
the planet gears and surround the entire planet

4

gear set.
The central shaft also forms the rotational point
for the hollow gear.

The hollow gear, planet carrier and sun wheel
are each connected to a shaft.

It is possible to achieve both large as well as
smaller high and low up and down gearing with a
planet gear set if one of the gear elements is
held fixed and the two others perform the task of
input and output.
When the planet carrier is held fixed, the direc­tion of rotation is reversed.
If two parts are held fixed, the planet gear blocks
and the ratio is 1:1.

- Hollow gear fixed

- Sun wheel driving =
large down gearing ratio

20

SP20-16

- Sun wheel fixed

- Hollow gear driving =
low down gearing ratio

SP20-17

SP20-18

- Planet carrier fixed

- Sun wheel driving =
reversal of direction of
rotation

It is possible to form additional transmission ratio versions from a combination of driving and braking
(holding fixed) parts

Hollow gear Sun wheel Planet carrier Ratio

Fixed Output Input High, fast

Output Fixed Input Low, fast

Input Output Fixed Fast, direction of rotation

reversed

Fixed Fixed Output No planet gear set

blocked

Input low Input normal Rotation superposed on that of

hollow gear, superposition of

speed (escalator effect)

Hollow gear

Planet gears with planet carrier

Sun wheel

Block diagram of input and output of a planet gear
set

Turbine shaft

SP20-20

The parts of the planetary gear set therefore
have to be braked or driven from outside.

If this is to operate properly, all the shafts of the
parts in question have to be led to the outside
and connected to countershafts.

This is solved in design terms by means of
intermeshed hollow shafts.

These are shaped on the outside like a bell
(clutch bells) and are positively connected to the
similarly shaped countershafts, depending on
their actuation.

The clutch bells in turn support in this case the
clutches and brakes.

During braking, the brakes are supported
against the gearbox housing (refer also to the
section on shift elements).

21

Planetary Gear Systems

Several planet gear sets are positioned one
after the other for an automatic gearbox in a
vehicle. It is then possible to combine the
required gearbox steps from this combination.

Wilson gearbox

Simpson gearbox

➙

➙

The different combinations and technical standard
designs are named after their inventors.

consists of 3 planet gear sets.
The first hollow gear, the second planet carrier and
the third hollow gear are permanently connected to
each other.
In addition, second and third sun wheel are perma­nently connected to each other.
The forward gears are driven through this double
sun wheel.

consists of 2 planet gear sets with a common sun
wheel.
The planet carrier of the one set, the hollow gear of
the other and the input shaft are permanently con­nected to each other.
The forward gears are each driven through the hol­low gears.
This design was often used in the age of three­speed automatic gearboxes.

Ravigneaux gearbox

➙

consists of 2 planet gear sets with a common planet
carrier.
This design is similar to that used in the 01M auto­matic gearbox of the SKODA OCTAVIA.

The planet carrier features two sets of planet gears:

- short planet gears with a large diameter which
mesh with a small sun wheel

- long planet gears with a small diameter which
mesh with a large sun wheel and the short
planet gears.

The Ravigneaux gearbox features only one hollow
gear which surrounds the short planet gears.

Power output is always through the hollow gear.
The design of the Ravigneaux gearbox makes it
possible to provide 4 forward gears and one
reverse gear.

Because of its compact design it is particularly suit­able for use in front-wheel-drive vehicles.

22

SP20-19

Multi-disc clutch

Shift Elements

Each gear features at least one shift element
which creates the power flow by means of fric­tion.

Multi-disc clutches are used in order to create
the power flow from the turbine shaft to the
planet gear set.

They possess internally-toothed and externally­toothed discs which are both connected to rotat­ing parts. They are interlaced in the form of
chambers. In the non-operated state, there is a
gap between them and they are filled with oil so
that they are also able to rotate freely.
The set of discs is compressed by a hydraulic
plunger which rotates together with its oil filling
which acts from the rear on the plunger.
The oil is therefore supplied through a hollow
shaft. The pressure on the multi-disc clutch is
released by means of springs when the clutch is
disengaged (compression springs or also disc
springs).
Ball valves (some in the plunger, the others in
the disc carrier) ensure that the pressure is able
to be reduced rapidly in the non-operated state
and the oil is able to flow off.

The disc carriers at the inner part as well as the
outer part support the discs by means of lugs,

which produces a positive connection.

Externally-toothed disc, positively
connected to outer part

Internally-toothed disc, positively
connected to inner part

Outer part

Ball valve

Externally-toothed
disc

SP20-22

Internally­toothed disc

Inner part

The externally-toothed discs are made of steel.
The internally-toothed discs are made of high­strength plastic.
At the same time, they perform the function of
the friction lining.
The supporting framework is made of cellulose.
The temperature resistance is achieved by
admixing aramide fibres, a high-strength plastic.
To influence the friction coefficient, minerals are
added for bonding phenol resin.

The number of discs differs considerably
depending on the gearbox version.
The play between the discs is of importance for
operation of the automatic gearshift and is fixed
as a result of the design.
It is set separately during installation.

We also find the principle of multi-disc clutch in
the 01M automatic gearbox of the SKODA
OCTAVIA.

Plunger

Disc carrier (clutch bell) for accommodating
externally-toothed discs

SP20-21

SP20-25

23

Shift Elements

Multi-disc brakes

The multi-disc brakes are used for holding a part
of the planetary gear set fixed. They are similar
to the multi-disc clutches and likewise feature
internally-toothed and externally-toothed discs.
The internally-toothed discs are likewise con­nected to the rotating part by means of lugs
whereas the externally-toothed discs are held in
position, supported at the gearbox housing.

During actuation, a hydraulic plunger com­presses the set of discs.
The hydraulic plunger does not move in contrast
to the multi-disc clutch.
In the case of the multi-disc brake as well, the
play between the clutches is of importance for
proper operation of the shift mechanism and is
set separately.

This type of brake is also used in the 01M auto­matic gearbox of the SKODA OCTAVIA.

Externally-toothed disc,
supported at gearbox

Internally-toothed disc, positively
meshed with rotating part

Gearbox
housing

Externally-toothed
disc, fixed

SP20-24

Band brakes

The band brake offers a further design possibility
of holding the elements of a planet set fixed.

The outer shape of the shaft is designed in a
similar way to a brake drum.
A steel brake band, as the braking element, is
closely wound around this brake drum, which
rotates freely in the non-operated state.
The brake band is supported at one end against
the gearbox housing.
At the other end, the piston force is active during
hydraulic actuation and brakes the drum until it
comes to a stop.

A disadvantage of the band brake is that large
radio forces act on the gearbox housing.

This principle is used, for example, in gearbox
001 of the Arosa.

Plunger

Internally­toothed disc

Rotating part

SP20-23

24

SP20-26

Overlap

During an electro-hydraulic gear change one
shift element is opened, another is closed.
This process occurs within fractions of a second.
During this operation, the torque transmitted by
the opening shift element drops. The torque
transmitted by the closing element increases.
The new gear meshes at the moment where the
torque at the engaging shift element is greater
than at the disengaging shift element.

p

P

p

P

0

P

n

This process is known as overlap.
In the case of the so-called zero overlap the
engaging shift element accepts as much torque
as the disengaging element releases. The result
is that the torque is retained.
The overlap control is performed solely by
means of hydraulic shift elements, actuated by
the electronic shift control unit.
The full working pressure is supplied to the
engaging shift element.

p = Pressure
t = Time

= Pressure pattern of disengaging shift

element at zero overlap

= Pressure pattern of engaging shift

element at zero overlap
= Negative overlap
= Positive overlap

P0= Point of zero overlap
Pn= Point of negative overlap
Pp= Point of positive overlap

t

SP20-27

In addition to zero overlap, there are also negative and positive overlaps which are applied specifically for
certain operating states.

Negative overlap

Engaging shift element accepts too late.
(In other words the pressure reduction of the first

shift element is too early in the case of a power
upshift/braking downshift
or
the pressure increase of the engaging shift ele­ment is too late during a power downshift/over­run upshift.
When the engine is operating under load, engine
speed rises as a result of the separation.
In overrun engine speed drops off).

Positive overlap

Engaging shift element accepts too early.
(In other words the pressure reduction at the dis-

engaging shift element is too late in the case of a
power upshift/braking downshift
or
the pressure increase of the engaging shift ele­ment is too soon during a power downshift/over­run upshift. The result is a brief blocking of the
gearbox and thus a drop in torque.
This can be advantageous if the engine has to
be reduced from a high to a lower speed).

25

Shift Elements

Freewheel

The overlap control can be simplified by provid­ing the assistance of freewheels.
The freewheel transmits a torque only in one
direction.
It rotates freely in the opposite direction.
It is used in order to simplify the technical design
of a shift mechanism without any interruption to
tractive force.
It permits exact shift transition without any partic­ular requirements regarding the control of the
engaging shift element.

Roller freewheel

Rollers are positioned in the gaps between the
inner and outer ring.
These move into the narrowing gaps in the lock­ing direction.
Inner and outer ring are connected as a result.
The springs press the rollers into the gap in
order to achieve reliable locking.
A roller freewheel is used, for example, in the
01M automatic gearbox of the SKODA OCTA­VIA.

When the vehicle is operating in overrun, the
power flow is reversed.
The freewheel would open as a result and not
permit any engine braking action (in a same way
as the freewheel of a bike).
That is why brakes or clutches are operated in
parallel to the freewheel.

Clamping body freewheel

This is a more involved design than the roller
freewheel but enables higher torques to be
transmitted within the same size of mechanism.
Dumbbell-shaped clamping bodies are posi­tioned between inner and outer ring within a
spring cage. They constantly make contact as a
result of the spring force. In the freewheeling
direction the clamping bodies are tilted and do
not impede the freewheel.
They move upright in the locking direction.
A clamping body freewheel is used, for example,
in the automatic gearbox 001 of the Arosa.

26

SP20-28

SP20-29

Gearbox Control

To simplify matters, we can say that four components are involved in the control logic and execution of a
modern automatic gearbox

Operating states

Driver

Driver decides when, to where, how quickly, sporty or economic

The "transmitters" are the accelerator pedal and the selector lever.

Operating states are responsible for producing the control pressures and the shift

travel.

Electronics driving resistances influence, whether uphill/downhill, towing a trailer,

driving into the wind, under power or in overrun.
Sensors pass the information to the control unit.

Hydraulics are responsible for producing the control pressures and the shift

travel.

This was not yet the case in early automatic gearboxes.
The logic of gear selection was performed hydraulically.

The operating states were detected by hydraulic, pneumatic and electrical components, converted into
pressures and the gear selection activated.

Electronics Hydraulics

Automatic gearbox

In the course of the development of electronics in vehicle engineering most of these components have
been replaced by corresponding electronic ones.
The hydraulic gearbox control has been transformed into the electronic gearbox control.

The shift elements are actuated by the electronics.
The electronic gearbox control has become the central element of the control logic and execution.
The shift points are formed from a large mass of information which describe the current operating and
driving situation (see also Determining shift points).

Exceptions

The main positions of the selector lever - P - R - N - D - continue to be passed in addition mechanically
by the selector lever to the selector slide valve in the hydraulic shift control unit, as before.
This ensures that the automatic gearbox can continue to operate even if the electronic control unit fails.

27

Gearbox Control

System overview of an automatic gearbox

The control unit is always located separately in the vehicle, not at the gearbox.
The installation point differs according to the vehicle model (e.g. in plenum chamber, in engine compart­ment, in footwell).

Engine load
Accelerator pedal
position

Gearbox speed

Vehicle speed

Engine speed

Position detection

Brake pedal opera­tion

Diagnostic

Kickdown

ATF temperature

The control unit determines the shift logic with permanent computer operations.
It uses these as a basis for actuating the control elements of the electronic gearbox control, the most
important of these being the solenoid valves which are located in the hydraulic shift control unit of

the gearbox.

connection

SP20-30

Hydraulic shift control
unit - solenoid valves

Selector lever lock

Starter lockout
Reversing light

Idle speed increase
Engine torque reduction

AC cut-off

The advantages of the electronic gearbox control compared to conventional hydraulic systems:

– Additional signals can be processed without any major additional effort.
– The hydraulic elements can be controlled more precisely.
– The effects of wear and tear can be compensated for by adaptive pressure control.
– The shift characteristics can be designed flexibly.
– The electronics offer enhanced protection against operating errors.
– Faults which occur can be bypassed to a certain extent to ensure that the vehicle

continues to operate.

– Faults which occur are stored in the fault memory for the Service sector.

The functions of the sensors and actuators of an automatic gearbox control are described in detail in
Self Study Programme 21, Automatic Gearbox 01M.

28

Communication with other vehicle systems

The electronic gearbox control is not a system which operates in isolation. It communicates with other
electronic systems in the vehicle in order to minimise the number of sensors, optimise smooth gear­shifts and enhance road safety.

A large number of signals are used in common
by the engine electronics and gearbox electron­ics, for example engine speed, load signal,
accelerator pedal position.
In order to minimise shift pressures during oper­ation of the shift elements (e.g. multi-disc
clutches, multi-disc brakes), the moment of a

Engine electronics

Running gear
electronics

gearshift is advised to the engine control unit.
That is why the control unit of the automatic
gearbox is linked by means of a direct line to the
engine control unit.
During the gearshift, ignition timing is retarded,
as a result of which engine torque decreases for
a short time.

Certain systems of the electronic gearbox con­trol conduct information transfer with various
running gear systems.
If a control cycle of a stability control system is
activated (e.g. electronic traction control or elec­tronic differential lock), the electronic gearbox
control does not carry out a gearshift.
In the event of a control cycle which is activated
when starting off (anti-slip control) the electronic
gearbox control makes use of second gear in
order to minimise the torque.
The lateral acceleration during tight cornering is
detected by a sensor and transmitted to the
electronic gearbox control. Gearshifts are sup­pressed during this time.

Air conditioning

If full engine torque is required during fast accel­eration, the magnetic coupling of the AC com­pressor is switched off.
The information for this is passed by the elec­tronic gearbox control to the AC control unit
once the kickdown switch is operated.

29

Gearbox Control

Emergency programme/Self-diagnosis

The electronic gearbox control features strategies in the
event of signal failures = emergency programme.

In the event of an input signal not being received, e.g. as a
result of a cable break, the system attempts to switch to a
substitute signal in order to maintain safe operation of the
vehicle.

Example:
The ATF temperature is detected by means of a tempera­ture sensor.
If the sensor fails, an empirical value of "warm gearbox
70°C" can be used.
The signal supplied by the engine coolant temperature sen­sor can also be used as a substitute.

The description of the sensors and actuators in Self Study
Programme 21 Automatic Gearbox 01M also contains the
relevant substitute signals.

1

2

3

4

5

6

7

8

9

C

O

HELP

Q

V.A.G.

1552

The gearbox control with diagnostic capability stores
any faults which occur in the emergency programme in the
fault memory.
This fault memory can be read at the diagnostic interface
using a fault reader.
It is thus possible to draw conclusions regarding the cause
of the fault in the Service sector.

A sporadic fault occurs only for a short time and then dis­appears again.

Various strategies are used depending on the type of fault:

– Control remains in emergency mode even if fault

does not occur again,

– Control returns to normal mode if fault no longer

occurs during several start operations.
The information remains stored in the fault memory, how­ever.

Emergency running

An emergency running mode is activated if essential sig­nals are not received or if the electronic gearbox control
itself fails.
In this case, a purely hydraulic mode is activated. The
selector lever remains coupled mechanically to the selector
slide valve in order to enable the vehicle to be driven in the
emergency running mode.
The automatic gearbox is in the N, R position or in a for­ward gear D depending on the position of the selector lever.
The torque converter lock-up clutch is switched off.

SP17-29

Note:
When carrying out service
work on an automatic
gearbox, therefore, al­ways read the fault memo­ry first of all before
carrying out any further
operations.

30

Hydraulic System

Hydraulic fluid circuit/hydraulic fluid pump

The torque converter, electronics and planetary
gear are ideally supplemented in the automatic
gearbox by the hydraulic system.

After all, the fluid in the automatic gearbox is the
working medium.

That is why particular importance is also attached
to the fluid in the automatic gearbox for, in the
absence of fluid, all of the functions would be lost
(for the importance of the fluid refer also to the sec­tion on automatic transmission fluid).

The hydraulic fluid is pressurized by a separate oil
pump and flows through the oil circuit.

The ATF pump used on almost all automatic gear­boxes is a crescent moon pump.
It is driven by the vehicle engine at engine speed.
Crescent moon pumps are rugged and reliable in
operation and produce the working pressure
required (up to approx. 25 bar).

Oil circuit (block diagram)

SP21-19

They ensure the oil supply of:

– the shift elements
– the gearbox control
– the hydrodynamic torque converter
– all the lubrication points of the gearbox.

The ATF is cooled in a small, separate circuit by
the engine coolant.

The pressure control and pressure distribution are
performed in the hydraulic shift control unit (usually
positioned below the gearbox).

A crescent moon pump is also fitted, for example,
to automatic gearbox 01M of the SKODA OCTAVIA
which is described in Self Study Programme 21.

The ATF circuit which is similar on all automatic
gearboxes, is also explained there.

SP21-18

Oil pump (ATF pump)

31

Hydraulic System

Hydraulic shift control unit

The hydraulic shift control unit is the control cen­tre for the ATF pressure.

The ATF pressure is controlled in this unit in line
with the control signals supplied by the electronic
gearbox control, and distributed to the shift ele­ments.

As a rule, the shift control unit consists of several
valve housings.
A valve housing is the common valve body for all
the valves which it contains (shift valves, control
solenoid valves, pressure control valves).
In addition, it contains the oil passages in accord­ance with the hydraulic diagram.
Oil passages in the valve housing are designed to
be free of intersections.
Any intersections required are created by holes
drilled in an intermediate block.
This makes it possible to form oil paths in various
valve housings placed one above the other.

The valves (solenoid valves) actuated electrically
by the electronic control unit, are placed onto the
valve housing from the outside.
They are therefore easily accessible for service
work and can be simply replaced.

Hydraulic shift control unit

SP20-32

Solenoid valves

Printed conductor along which the
signals flow into the solenoid valves

In addition to its electrical connections to the elec-

tronic control unit, the hydraulic shift control unit is
also linked mechanically to the selector lever by
means of a hand slide valve.

The hydraulic shift control unit is usually installed
below the gearbox.
In this case, the gearbox housing then contains
part of the oil passages.

The oil passages can also be designed as a sepa­rate oil passage plate.

32

SP20-33

Oil passages in gearbox housing

Diagram of hydraulic system

The hydraulic diagram is a simplified detail from the
hydraulic plan of an automatic gearbox.

We can use this diagram to explain the complicated
hydraulic control labyrinth.
Two shift elements are shown. Depending on the design
of a gearbox, this may be six to eight friction elements
(clutches and brakes) in a modern four-speed gearbox.

Shift elements

The diagram shows the valves in the off position

Oil pump

Pressure control
valve

Control solenoid valve

Shift solenoid valve

Shift valve

Zero outflow

O O

Restrictor

SP20-34

Induction

Working pressure for shift elements

Working pressure for torque converter lock-up clutch

Shift valve pressure

Control valve pressure

Modulating pressure

Shift pressure

Shift pressure stabilised

Lubrication pressure

Control pressure for torque converter lock-up clutch

33

Hydraulic System

Pressures in the hydraulic system

The oil in the hydraulic system has to be present
at different pressure levels. Pressure control
valves and control solenoid valves are used to
produce the pressure stages required.

Working pressure

The working pressure is 25 bar, and is thus the
highest pressure in the hydraulic system.
It is produced by the oil pump and also exists
directly downstream of the latter.
It is stabilised by the working pressure control
valve by means of a controlled zero outflow.
The pressure is controlled by control pulses of the
electronic gearbox control in line with the gear
engaged.
Depending on the gear to be engaged the working
pressure is distributed to one or more shift ele­ments.
This distribution of pressure is performed by a
shift valve.
The working pressure exists at a relevant shift
element when the gear is being engaged.

SP20-37

Working pressure control valve
(a pressure control valve)

Shift valve pressure
Control valve pressure

The shift valve pressure is set to 3 - 8 bar by
means of a pressure control valve.
It supplies the electrically controlled shift solenoid
valves.

Important!

Shift solenoid valves use the shift valve pressure
to control downstream shift valves, which in turn
control the shift elements (refer also to shift exam­ple).

The control valve pressure is likewise set by
means of a pressure control valve and is 3 to
8 bar.
It supplies a control pressure through a control
solenoid valve to a downstream pressure control
valve, for example for the torque converter lock­up clutch.

Shift solenoid valve

Pressure control
valve

Pressure control
valve

Control solenoid
valve

Shift element

Shift valve

SP20-38

Pressure control
valve

34

Modulating pressure

The modulating pressure is proportional to the
engine torque, it reflects the engine load.
The modulation valve (a control solenoid valve) is
actuated by the electronic gearbox control on the
basis of the information supplied by the engine
electronics, and produces the modulation pres­sure.
This is 0 to 7 bar.
The modulation pressure flows to the working
pressure control valve and thus influences the
level of the working pressure.

Shift pressure
Lubrication pressure

The shift pressure is 6 to 12 bar. It is used during
the gear change at the shift element to be oper­ated. The shift pressure is set by the electronic
gearbox control through a control solenoid valve
and a pressure control valve.
After the gearshift is completed, it is substituted at
the shift element by the working pressure.

SP20-39

The lubrication pressure is 3 to 6 bar. It supplies

the torque converter. The hydraulic fluid flows
through the torque converter, the ATF cooler and
through all the lubrication points of the automatic
gearbox.

Pressure for lock-up clutch

The pressure is set by means of a control sole­noid valve and a pressure control valve and is
controlled by the electronic gearbox control.
The pressure is set in line with the torque to be
transmitted.

SP20-40

SP20-44

35

Hydraulic System

Hydraulic shift elements

Solenoid valves are used in the electronically control­led automatic gearbox as hydraulic shift elements
(shift solenoid valve, control solenoid valve).
In addition, shift valves which operate only hydrauli­cally, are also used.

Shift solenoid valve

P

A

O

SP20-41

Shift valve

Shift valve pressure

Valve plunger

Armature

Coil

Shift solenoid valves pass on the oil pressure to a
shift valve or reduce the oil pressure. In other
words, they switch on or off and cause the shift
elements to switch over, for example to initiate the
shift procedure.

They are closed in the off position by spring force.
The armature is connected to the valve plunger.
When actuated by the electronic control unit, the
armature is pulled against the spring force.

The valve plunger opens the passage from P to A
for the shift valve pressure and closes off the out­let O.

Shift solenoid valves are actuated by means of a
digital shift signal.
The shift valve pressure acts as a control pres­sure on the shift valve.

The shift valve is a valve which operates purely
hydraulically. Its purpose is to distribute the pres­sure to the shift elements.

Off position

Shift position

36

As a rule, it has only two shift positions which are

A

X

O P L

A

X

O P

L

SP20-36

operated by one or two control pressures.
In the off position, the working connection A is

linked to outlet O, the shift elements are thus
pressureless.

In the working position, the control pressure is
effective at connection X, pressure P is switched
through to connection A, outlet O is shut off. Out­let L acts only as a compensation port.

The majority of shift valves are designed as slide
valves and are therefore often also called slide
valves or shift slide valves.

Example of operation of shift solenoid valve
and shift valve - block diagram

A

O P

A

X

O P

Working pressure

SP20-35

Off position

Working position

Shift valve pressure

X

The example of the operation is intended to
clearly show us that the working pressure is not
supplied to a shift element through the solenoid
valve.

Off position

The shift solenoid valve is not actuated. No con­trol pressure (shift valve pressure) exists at the
shift valve.
The zero outlet is open.

Working position

The shift solenoid valve is actuated by the elec­tronic control unit of the automatic gearbox, it is
operated electrically.
The solenoid valve attracts a valve plunger and
opens the passage for the flow of the shift valve
pressure to the shift valve.
The piston (slide) in the shift valve is now moved
hydraulically.
Consequently, the zero outlet is shut off, the con­nection for the working pressure is opened.
The working pressure now acts fully on the shift
element (clutch or brake, depending on the con­trol logic).

Control solenoid valve

Control valve pressure

P

O

A

Valve plunger

Armature

Coil

SP20-42

Control solenoid valves set a stepless oil pres­sure.

They are shut-off valves toward a zero pressure,
pretensioned by spring force.
When actuated, the armature is pulled against the
spring force and the valve plunger opens the out­let O.
Consequently, the oil pressure drops at A, all the
more the greater the actuation current, which thus
produces a stepless control.

Low amperage = high pressure
High amperage = low pressure

Control solenoid valves are always used in combi­nation with a restrictor and are supplied with the
control valve pressure.
They do not control the oil pressure of a shift ele­ment directly, but supply the control pressure
which acts through A on a downstream pressure
control valve (e.g. modulating pressure).

37

?

Test Your Knowledge

Which answers are correct?
Sometimes only one,
but perhaps also more than one - or all of them!

Please complete these points ......................

1. In a manually shifted gearbox it is the mechanical
clutch which transmits the engine torque to the
gearbox.
In an automatic gearbox this function is performed by the

.........................................

?

2. Design features of an automatic gearbox are:
A. The hydraulics perform the task of synchronising the wheel speeds.

B. It is possible to shift gears without any interruption to the power flow.
C. All gear pairs are constantly meshed.

3. The mechanical basis of almost all automatic gearboxes are

............................

4. A special design of ...................................... is the Ravigneaux gearbox

A. It has 3 planet gear sets.
B. It has 2 planet gear sets with a common sun wheel.
C. It has 2 planet gear sets with a common planet carrier.

5. The shift points are determined by the electronic gearbox control in a conventional way using two
parameters.

These are .......................... and .....................

6. The oil in an automatic gearbox is often characterized by the abbreviation .........

In addition to lubrication, it has to perform a number of other important tasks.
Which answers are not correct?

A. Transmitting forces
B. Performing the synchromesh work
C. Storing heat
D. Performing gearshifts

38

?

7. Which statement is correct?
A. In an automatic gearbox there are only electro-hydraulic functions.

B. In an automatic gearbox too, important selector lever positions are transmitted mechanically to

the hydraulic shift control unit.

8. Which valve passes the working pressure of ....... bar to the shift elements?

A. The control solenoid valve
B. The shift solenoid valve
C. The shift valve

9. Complete the missing lines and valves in the hydraulic diagram.

10. The electronic gearbox control has a .................................

If, for example, a customer complains of poor performance, the first job to do is therefore ........

......................... .........

11. When does a torque converter operate only as a clutch?
A. When the turbine wheel is stationary

B. At maximum torque boost
C. When pump speed and turbine speed are practically the same.

7. B; 8. approx. 25, C; 9. Page 33; 10. Diagnostic capability, to interrogate the fault memory; 11. C.

4. Planetary gear, C; 5. Road speed, accelerator pedal position; 6. ATF;B,C;

1. Torque converter; 2. B;C; 3. Planetary gear

Answers:

39