NEW
SP29-06
With the OCTAVIA 4 x 4, SKODA is enlarging
its production range with a vehicle offering
the most modern permanent all-wheel drive
technology.
Classical all-wheel drive concepts - still found
today in a large number of off-road vehicles in many cases make use of a rigid connection
which is engaged by means of a handshift.
A new technical feature for permanent allwheel drive with an additional connection at
the rigid through-drive to the rear, operated
independently of the driver, was the viscous
coupling, as fitted for example to the VW
syncro.
This was in the position only to detect wheel
slip, but not the cause of it. To ensure reliable
braking in such cases, both axles had to be
decoupled by means of a freewheel. When
reversing, the axles were again connected by
means of a lock.
A significant advance in modern all-wheel
technology has been achieved with the
development of the Haldex coupling.
The Haldex coupling can be controlled.
A processor analyses additional information
during the control cycle. It is no longer the
wheel slip alone which is decisive for the
distribution of the tractive forces, but also the
dynamic state of the vehicle.
The processor accesses the ABS wheel speed
sensors and the engine management system
(accelerator pedal signal) through the CANBUS.
These data provide the processor with the
information which is required regarding
vehicle speed, cornering, deceleration or
acceleration, and enables it to react optimally
to the particular situation.
Advantages of the Haldex coupling
– Permanent all-wheel drive with
electronically controlled multi-plate
coupling
– Front-wheel drive characteristics
– Rapid response (power transmission)
– Instant decoupling of both axles
– No stresses in the drive train when parking
and manoeuvring
– No restrictions when towing vehicle with
front wheels raised
– Can be fully combined with wheel slip
control systems such as ABS, EDL, TCS,
EBD and ESP
– Possibility of simple test of brakes and
performance on roller dynamometer
2
11
12
13
14
16
Contents
All-wheel Drive 4
Manual Gearbox 6
Rear Final Drive 8
Cardan Shaft 10
Modifications to 4x4 Vehicle 11
Rear axle
Fuel tank
Vehicle floor
Exhaust system
Haldex Coupling 14
System description
Mechanical components
Multi-plate coupling
13
20
Hydraulic System 22
System Overview 28
Sensors 30
Control Unit 36
Actuators 37
Self Diagnosis 39
Function Diagram 40
Driving Situations 42
Test Your Knowledge 44
You will find notes on inspection and
maintenance, setting and repair instructions
in the Workshop Manual.
Service
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Service
3
All-wheel Drive
The 4x4 drive train
The 4x4 drive train is based on the
components of the A platform vehicles of the
Group.
A characteristic feature is the permanent allwheel drive with electronically controlled
multi-plate coupling - the Haldex coupling.
The new coupling is a compact unit which is
connected to the rear final drive.
Compared to front-wheel drive vehicles,
the 4x4 drive necessitated a number of
modifications or involved the introduction
of new assemblies.
5-speed manual gearbox with bevel box
The 5-speed manual gearbox is fitted
additionally with a bevel box.
The torque is transmitted from the front-wheel
drive to the rear-wheel drive by means of a
cardan shaft.
The cardan shaft is a two-section design. It is
attached at the manual gearbox by means of a
flexible joint, and at the rear final drive by
means of flexible joint with vibration damper.
SP29-64
4
The engine torque is transmitted through the
manual gearbox with the front axle differential
through the bevel box to the cardan shaft.
The cardan shaft is connected to the input
shaft of the Haldex coupling.
In the Haldex coupling, the input shaft is
separated by the output shaft to the bevel box.
The torque is transmitted on through the
differential of the rear final drive to the rear
drive shafts.
The torque is only transmitted to the rear final
drive if the multiple plates of the Haldex
coupling are closed.
SP29-07
SP29-09
Final drive with Haldex coupling and bevel drive
5
Manual Gearbox
5-speed manual gearbox 02C
All-wheel drive
The 5-speed manual gearbox 02C is a gearbox
which has been specially developed for the
4x4 model.
The ratios of the individual gears and of the
final drive have been matched to the engine
output.
The clutch is operated hydraulically.
The bevel box is attached to the side of the
manual gearbox and connected to the
differential of the manual gearbox.
The differential and the bevel box are
mounted in the same housing in taper roller
bearings.
6
SP29-20
The bevel drive has to be set.
An important factor is the assignment of the
rear final drive to its bevel drive!
The ratio of the front bevel drive to the rear
bevel drive must always be 1.
Teeth of driven gear z
Reduction i =
Teeth of driving gear z
z
2
st
1
gear 33 10 3.300
nd
2
gear 35 18 1.944
rd
3
gear 34 25 1.360
th
4
gear 35 34 1.029
th
5
gear 36 43 0.857
Reverse 17
36
Final drive 63 16 3.938
Speedo 13 22 0.591
Front/rear bevel
drive
17 : 27 x 27 : 17 1
z
10
20
1
2
1
i
3.060
SP29-64
5
3
4
2
1
R
The shift mechanism makes use of a cable
shift.
The internal shift mechanism is similar to that
of manual gearbox 02J.
SP29-19
Note:
The function description of the cable
shift and the gearshift mechanism can
be read up in SSP 18.
7
Rear Final Drive
The rear final drive
is always assigned to the manual gearbox.
The assignment is carried out by means of
code letters.
Final drive and
differential
The final drive of the rear axle consists of an
integrated assembly incorporating
Cross member
Connection to
subframe
Haldex coupling
The Haldex coupling is connected electrically
to the vehicle wiring loom.
SP29-21
Haldex coupling
Bevel drive and
Differential.
The rear final drive is connected to the
subframe with the rear axle by means of a
cross member.
Haldex coupling and rear final drive have
separate oil fillings.
Final drive: Gear oil
Haldex coupling: High-performance oil
8
The function of the Haldex coupling does not
necessitate any further connections, e.g. for
operation.
Note:
You can find capacities and
specifications of the oils in the
relevant Workshop Manual OCTAVIA.
Differential
Haldex coupling
The bevel drive is formed from the shaft bevel
pinion and the head bevel pinion.
The shaft bevel pinion is part of the Haldex
coupling whereas the head bevel pinion
belongs to the final drive.
The housing of the Haldex coupling is bolted
to the housing of the final drive. This bolted
connection also determines the play of the
bevel drive when it operates.
Bevel drive with Haldex coupling
Careful alignment of shaft bevel pinion to
head bevel pinion is an essential requirement
for long operating life and smooth running of
the bevel drive.
That is why, the shaft bevel gears and head
bevel gears are matched to each other during
the manufacturing process and checked for
optimal positioning of the contact pattern and
for quiet running.
Final drive
Head bevel
pinion
Shaft bevel pinion
SP29-22
Note:
For this reason, always refer to the
information regarding realigning a
bevel gear set.
You can find this in Workshop Manual
OCTAVIA, 5-Speed Manual Gearbox
02C All-wheel Drive.
9
Cardan Shaft
Flexible joint to manual
gearbox
The cardan shaft is a two-section design.
The cardan shaft is attached at the manual
gearbox by means of a flexible joint.
It is attached at the rear final drive (Haldex
coupling) by means of a flexible joint with
vibration damper.
The front and rear cardan shaft tubes are
connected by means of flanges at a CV joint.
The cardan shaft is attached downstream of
the CV joint to the middle bearing at the
vehicle floor.
SP29-65
CV joint
Flexible joint with
vibration damper
The entire cardan shaft is balanced during
manufacture in order to ensure optimal
smooth operation.
It is not possible to balance the entire cardan
shaft with workshop equipment.
If the front or rear cardan shaft tube is
damaged, it is therefore always necessary to
replace the entire cardan shaft.
Note:
Mark the position of all the parts
before removing a cardan shaft.
Re-install in the same position
otherwise the imbalance will be
excessive. This could result in damage
to the mountings and rumbling
noises.
Always store and transport the cardan
shaft in the extended position.
10
Modifications 4x4 Vehicles
Modifications compared to front-wheel drive
The 4x4 concept necessitated
– a new rear axle
– redesigning the fuel tank
– a new vehicle floor
– adapting the exhaust system
Bonded rubber bush
The rear axle
– A double wishbone trailing arm axle
(TADW axle).
Shock absorber
Haldex coupling
Wishbone
Anti-roll bar
Cross member
Subframe
Trailing arm
– An anti-roll bar is provided at the subframe
of the axle to stabilise the vehicle.
SP29-03
– The TADW axle is attached by means of
the subframe (4-point attachment) and the
track-correcting bonded rubber bushes
fitted at each trailing arm.
– The subframe is a very flat design in order
to maintain the existing available space in
the interior.
– The rear final drive is bolted to a cross
member which is attached to the
subframe.
– Shock absorber installation position
(approx. 45˚)
– The design features of the axle attachment
for improving comfort (acoustic
decoupling to body and separate
arrangement of spring and shock
absorber), familiar from front-wheel
drive models, have been retained.
– Ground clearance increased by 23 mm.
11
Modifications 4x4 Vehicles
Fuel tank
Suction spray
pump in returnflow line
Fuel gauge
sender G
Reservoir housing
with fuel pump
The fuel tank has been provided with a
“tunnel” in order to provide the space
required for the cardan shaft running to the
rear axle.
This results in a “two-section tank”.
For this reason, in models fitted with petrol
engines, there is a suction spray pump in the
left tank area, which pumps fuel out of the left
side of the tank into the right side.
The suction spray pump is powered by the
fuel return flow from the two-stage fuel pump.
Tunnel
Fuel gauge sender
G169
SP29-04
On models fitted with a diesel engine, an
electric fuel pump pumps fuel from the left
chamber of the tank into the right chamber.
A fuel gauge sensor is provided in each
chamber of the fuel tank.
These are operated in series.
Reserve 1 + reserve 2 = total reserve
The evaluation is carried out in the
combination processor of the dash panel
insert.
J17
G Fuel gauge sender
G1 Fuel gauge
G6 Fuel pump
G169 Fuel gauge sender 2
J17 Fuel pump relay
J218 Combination processor in dash panel insert
J220 Motronic control unit
S Fuse
12
31
G6
+15 J220 +30
S
G G169
M
G1
J218
SP29-05
Vehicle floor
Spare wheel well
Wiring loom of
Haldex coupling
SP29-42
The spare wheel well on 4x4 models has been
repositioned 250 mm to the rear.
This provides the space required for attaching
the trailing arms at the vehicle floor.
Adaptation of exhaust system
The all-wheel drive with the cardan shaft and
new rear axle has necessitated modifications
to the exhaust system.
The front exhaust pipe has to be routed
around the cardan shaft.
The wiring loom for the Haldex coupling is
routed through the inside of the spare wheel
well.
This ensures that it is adequately protected
against damage from the road surface.
Bypass for cardan
shaft
Exhaust system of
1.9-ltr. TDI
SP29-43
At the rear axle, it is not possible to route the
rear exhaust pipe over the axle, as is the case
at the front-wheel drive, but it has to be routed
below the axle.
The version of front exhaust pipe used always
depends on the particular engine fitted.
13
Haldex Coupling
System description of Haldex
multi-plate coupling
The Haldex coupling is an electronically
controlled electro-hydraulic coupling.
The complete system is installed between the
cardan shaft and the rear axle differential, and
operates as an interaction of the mechanical
components, the hydraulic components and
the electronic control.
The multi-plate set is located inside the
housing, and runs in its own oil bath. The
multi-plate set is compressed by the hydraulic
pressure. It is thus able to transmit a variable
torque to the rear axle.
The magnitude of the torque is proportional to
the pressure applied to the multi-plate
coupling.
Two axial piston pumps provide the pressure
required in the working piston to compress
the multi-plate set. These pumps are driven by
an eccentric plate (axial cam plate) by means
of the differential speed between the input
shaft and the output shaft of the Haldex
coupling.
An electro-hydraulic valve (control valve)
steplessly alters this pressure.
The Haldex coupling does not have any
sensors of its own, with the exception of a
temperature sensor (required for
compensating for the temperature-dependent
oil viscosity).
Mechanical
components
Hydraulic
components
This information comprises
– wheel speed of each individual wheel
– engine torque
– engine speed
– driving state (straightahead driving,
overrun, braking, ABS)
– accelerator pedal position/throttle valve
position
Electronic
components
SP29-40
The electronic control unit (four-wheel drive
control unit) makes use of the existing
information in the vehicle for controlling the
pressure of the Haldex coupling. This
information is provided over the CAN-BUS.
14
The situations detected include cornering,
manoeuvring mode, acceleration phase,
different wheel circumferences. The required
stiffness of the Haldex coupling is controlled
in line with the driving state detected.
The mechanical components with the rotating
and moving parts, include:
– the input shaft with externally-toothed disc
carrier
– the internally-toothed and externally-
toothed discs
– the eccentric plate (axial cam plate) at the
internally-toothed disc carrier
– the pressure rollers for the annular pistons
– the shaft bevel pinion with internally-
toothed disc carrier
Multi-plate coupling
Eccentric disc
(axial cam)
Pressure roller
Pressure limiting
valve
Shaft bevel pinion outlet
Four-wheel drive
control unit
Positioning motor
Accumulator
Input shaft
Oil filter
Annular pistons of
axial piston pumps
Electric oil
pump
Temperature sensor
Control valve
hydraulic system includes
The
– the pressure limiting valve
– the pressure valves
– the accumulator
– the oil filter
– the annular pistons (one working piston,
two pump pistons)
– the control valve
SP29-71
electrical system includes
The
– the four-wheel drive control unit
– the electric oil pump
– the positioning motor for the control valve
– the temperature sensor
15
Haldex Coupling
Mechanical components
The general design of the Haldex coupling at
a glance
Housing of Haldex coupling
Internally-toothed disc
Axial needle bearing
Shaft bevel pinion outlet
(part of rear bevel gear drive,
which drives the rear axle)
16
Externallytoothed disc
Externally-toothed disc
carrier
17
Pressure roller to
working piston
Pressure roller
(inner pump piston)
Working piston
(annular piston)
Outer pump piston
(annular piston)
Inner pump piston
(annular piston)
Flange to cardan shaft
Input shaft
Pressure plate
Internally-toothed
disc carrier
Pressure roller
(outer pump piston)
Eccentric disc (axial cam disc)
Hydraulic oil drillings
SP29-02
Hydraulic block of
Haldex coupling
Haldex Coupling
Mechanical components
The input shaft is connected to the guide plate
for the pressure rollers and the outer-toothed
disc carrier.
Three pressure rollers, each offset 120˚, are
assigned to each piston. This ensures static
stability when transmitting the pressure.
During each revolution, the pressure rollers
for the pump pistons and for the working
piston also rotate.
SP29-23
Internally-toothed disc carrier
with eccentric plate and multi-disc set with pressure
plate
The eccentric plate is part of the internallytoothed disc carrier. It is permanently
mounted on the shaft of the bevel pinion.
The eccentric disc has three cams, each offset
axially 120˚ - which is why it is also known as
an axial cam disc.
The system then operates in principle like a
distributor injection pump.
Eccentric plate
Pressure plate
SP29-24
Guide plate
Pressure roller
Outer-toothed
disc carrier
SP29-25
Input shaft
with guide disc for pressure rollers and outertoothed disc carrier
When the car is accelerated, the pressure
rollers of the pump pistons move against the
eccentric disc which is either still stationary or
rotating only slowly. A pump movement thus
begins, in other words the purely rotational
movement of the pressure rollers is converted
in the guide plate into a rotational and lifting
movement as a result of the axial cams on the
eccentric plate.
The rotary/lifting movement is transmitted by
the pressure rollers to the pump piston. These
in turn then perform only a lifting movement
and increase the pressure which then acts on
the working system.
18
The mechanical pump rhythm
In the same way as the eccentric plate, the
pressure plate on which the three pressure
rollers of the working piston act, also has
three axially offset raised phases.
Each raised phase of the pressure plate is
always positioned opposite a valley on the
eccentric plate.
The pressure rollers of the two pump pistons
1 and 2 are, in addition, positioned with a
phase offset.
Pressure plate
SP29-26
Eccentric plate
1
2
3
60°
1 = Lift contour of pressure roller of outer pump
piston
2 = Lift contour of pressure roller of inner pump
piston
3 = Lift contour of pressure roller of multi-disc set/
working piston
An even pressure pattern is achieved by each
of the 3 pump lifts, which are consequently
performed with a phase offset.
At the moment when the phase-offset pump
pistons 1 and 2 are not producing a pressure
(range “x”), the pressure plate for multi-disc
set 3 in turn has a raised phase.
-X-
120°
180°
SP29-27
SP29-28
1 = Pressure roller of outer
pump piston
3 = Pressure roller
of working
piston
2 = Pressure roller of
inner pump piston
The pressure acting on the pressure roller of
the working piston is increased.
As a result, the multi-disc set remains fully
pressurized and “all-wheel drive” is assured.
19
Haldex Coupling
The multi-disc coupling
The operating principle of the multi-disc
coupling is the same as that as you are
familiar with from the automatic gearbox
(see SSP 20).
– Externally-toothed discs positively
connected to the externally-toothed disc
carrier
– Internally-toothed discs positively
connected to the internally-toothed disc
carrier
SP29-32
Externallytoothed disc
Internally-toothed
disc
The multi-disc set constantly runs in oil.
The internally-toothed discs have a smooth
surface on both sides.
In contrast, the externally-toothed discs have
grooves on the surface of both sides.
If the disc set is pressed together as a result of
the pressure of the working piston, the oil is
thus able to flow off rapidly through the
grooves.
On the other hand, the disc set is constantly
lubricated in order to minimise wear.
Pressure plate
SP29-33
The multi-disc set of the Haldex coupling
consists of 7 externally-toothed discs and 6
internally-toothed discs.
The set of 6 internally-toothed discs is
supplemented
– by the pressure plate on which the
pressure rollers of the working piston act,
– by the rear contact plate which runs in the
axial needle bearing in the housing.
Externally-toothed disc carrier
with externally-toothed discs
Axial needle
bearing
Internally-toothed
Shaft of
bevel pinion
disc carrier with
internally-toothed
disc
Pressure plate
Pressure roller of
working piston
SP29-34
Input shaft
20
The hydraulic block
M
The input shaft runs through the middle of the
hydraulic block.
The pistons (1 working piston, 2 pump
pistons) are positioned centred around the
shaft.
Input shaft
Working piston
SP29-29
Outer pump
piston
Inner pump
piston
The hydraulic block contains the hydraulic
drillings to the annular pistons and to the
connection points to the oil pump, to the
control valve and to the safety valves.
The hydraulic circuit is formed by these.
Hydraulic block with working
piston and pump pistons
Connection of four-wheel drive
control unit
SP29-30
M
Electric oil pump
Control valve
Pressure limiting valve
Valve (suction valve, pressure valve)
Block diagram of hydraulic circuit
SP29-31
21
Hydraulic System
Pressure valves
Pressure rollers
Eccentric disc
Pressure limiting valve
Control
valve
Positioning
motor
Accumulator
Axial needle
bearing
Multi-disc
coupling
Pump pistons
Hydraulic system - pressureless -
The hydraulic system is pressureless and the
multi-disc coupling is thus not operating.
There is also no pre-pressure in the hydraulic
system. The control valve is open. The
eccentric disc is running empty and the
pressure rollers of the pump pistons are not in
contact.
These conditions exist:
– when the vehicle is stationary or moving
and the ignition is off
– when towing vehicle with front wheels
raised (engine off and thus ignition off)
– during a brake test on the roller
dynamometer (engine off and thus
emission off) when front wheels are
driven.
Suction valves
Working piston
Filter
Electric oil
pump
Strainer
pressureless
Pressure is built up as a result of the speed
difference between the input shaft and the
output shaft only when the ignition is
switched on.
The oil pressure is regulated by valves.
The pressure limiting valve determines the
maximum pressure at the multi-disc set while
the control valve determines the torque
transmitted through the multi-disc coupling.
Note:
For the schematic presentation of the
hydraulic system, the pump pistons
have been shown positioned next to
each other and the eccentric plate
with two cams and two valleys.
As a reminder:
The pump pistons are positioned
phased-offset.
The eccentric disc has three cams
offset by 120˚ with a lift of 1.2 mm.
SP29-35
22
Pressure rollers
Pressure valves
Pressure limiting valve
Control
valve
Positioning
motor
Accumulator
Multi-disc
coupling
Pump pistons
Pressure build-up in hydraulic system as a
result of electrical oil pump (pre-pressure)
The Haldex coupling engages within a very
short time. The maximum pressure is
available at the latest after a rotational angle
of 45˚.
On the other hand, the multi-disc set has to
have a certain clearance if the coupling is to
be “inactive”, but it must also be possible,
however, to eliminate this clearance very
rapidly.
That is why the system operates with a prepressure.
Suction valves
Working piston
Filter
Electric oil
pump
Strainer
As a result, the cylinders behind the pump
pistons are supplied with oil and the pressure
rollers are pressed and held against the
eccentric disc.
At the same time, the oil flows through the
control valve and through the pressure valves
to the working piston. This piston likewise
makes contact. As a result of this prepressure, the play which exists in the multidisc set is eliminated. This ensures rapid
response of the coupling.
Pre-pressure
Pressureless
SP29-36
The pistons of the pump pistons are a floating
design and only make contact once pressure
is supplied by the electric oil pump. This
pump only operates if the ignition is switched
on and if engine speed is > 400 rpm.
The oil pump draws oil out of the pressureless
chamber of the coupling housing through a
strainer and pumps it through a filter through
the suction valves to the pump pistons.
The pre-pressure of 0.4 MPa (4 bar) is
determined by the accumulator. A further task
of the accumulator is to even out any pressure
variations.
23
Hydraulic System
Pressure valves
Working piston
Pressure roller
Pressure plate
Pressure limiting valve
Control
valve
Positioning
motor
Accumulator
Multi-disc
coupling
Pressure build-up in hydraulic system through
pump pistons (control valve closed)
The oil pressure produced by the pump
pistons flows through the pressure valves to
the working piston and to the control valve.
The closed control valve acts as a resistance
and the pressure in the cylinder of the working
piston rises.
The working piston is moved and presses
against the multi-disc coupling through the
pressure rollers and pressure plate.
The multi-disc coupling is closed and thus
creates the connection between the input
shaft and the output shaft.
Pump piston
Pressure
Pre-pressure
Pressureless
The pressure at the multi-disc coupling is
determined by the control valve.
The positioning motor, which is operated by
the four-wheel drive control unit, alters the
position of the control valve. If the control
valve is fully closed, the maximum pressure is
acting on the multi-disc coupling.
The maximum pressure is determined by the
pressure limiting valve.
SP29-37
The torque is transmitted to the rear axle.
24
Multi-disc
coupling
Pressure valves
Control
valve
Accumulator
Pump pistons
Working piston
Pressure build-up in hydraulic system through
the pump pistons (control valve open one
third)
The pressure produced by the pump pistons
flows through the pressure valves to the
working piston and at the same time into the
control valve.
The control valve is opened one third by the
four-wheel drive control unit, in line with the
actuation. Part of the oil is able to flow back
through the accumulator into the oil chamber.
Pressure
Oil return flow
Pressureless
SP29-38
This results in a reduction in pressure so that
the coupling permits only a limited
transmission of torque.
Consequently, the coupling can also permit
reduced all-wheel drive in certain driving
situations.
25
Hydraulic System
Control
valve
Accumulator
Multi-disc
coupling
Pressure build-up in hydraulic system through
the pump pistons (control valve opened)
The pressure required for the particular
driving situation is determined by the fourwheel drive control unit.
The control valve is open. The oil now flows
through the control valve and the accumulator
back into the oil chamber.
Consequently, no build-up of pressure takes
place at the working piston. The multi-disc
coupling is open and there is also no
transmission of torque.
The accumulator maintains the pre-pressure
in the return-flow line of the control valve.
A pre-pressure of 0.4 MPa (4 bar) exists in the
return-flow line.
Working piston
Pump pistons
Pressure
Pressureless
The pump pistons operate practically only for
the pre-pressure.
Note:
Pre-pressure is necessary for the rapid
response of the Haldex coupling. The
pre-pressure eliminates the play in the
multi-disc set.
SP29-39
26
Summary of operating sequence of Haldex
coupling
Shaft 2
Eccentric disc
Pressure roller of
working piston
Working piston
Shaft 1
We can recognize the operating principle from
the mechanical design and the description of
the hydraulic system:
In the initial position, the input shaft 1 and
output shaft 2 are rotating at the same speed.
The hydraulic coupling is thus inactive. The
coupling is released.
Once a difference in speed exists between
shaft 1 and shaft 2, the pressure rollers and
the pump pistons at the eccentric disc begin to
pulse. Consequently, oil is drawn into the
cylinder behind the pump pistons.
At the same time, the pressure produced by
the pump pistons passes through the pressure
valves to the working piston.
The working piston compresses the multi-disc
set through the pressure rollers and pressure
plate. The coupling now has a positive
connection.
Pressure
plate
Pressure
roller
Pump pistons
SP29-02
If a difference in speed remains at the shafts,
the pump pistons continue to pulse and pump
oil to the working cylinder.
The working piston compresses the multi-disc
set with greater force, which results in an
increase in the torque transmitted.
If there is an increase in the torque
transmitted, the difference in speed is
reduced.
The coupling is again inactive.
Only the pre-pressure is maintained in the
hydraulic system.
The pressure build-up and the torque
transmission can be adapted to match the
particular driving situation by the four-wheel
drive control unit.
27
System Overview
Engine speed sender G28
Accelerator pedal position sender G79/G185
Engine control unit
+ Engine torque
Wheel speed sensors G44 - G47
Longitudinal acceleration sender G249
Brake light switch F
Handbrake indicator switch F9
ABS with EDL control unit J104
Note:
The signal for the brake light switch
as a rule passes along the CAN
databus; in the emergency mode, it
passes over a direct wire into the fourwheel drive control unit.
28
CAN databus
Handbrake indicator switch F9
Brake light switch F
Hydraulic temperature
sender G271
Four-wheel drive control unit J492
Diagnostic
connection
Oil pressure positioning
motor V184
Haldex coupling pump V181
SP29-08
29
Sensors
Note:
A number of sensors and control units
of other systems are used for
controlling the Haldex coupling
system.
You will be already familiar with the
design and operation of these.
For this reason, the section which
follows deals only with the effects
when all-wheel drive is active. The
control algorithms of the four-wheel
drive control unit are based as a
general rule on the processing of all
the signals.
Use of signal for 4x4 electronic control Effect in the event of signal
Engine control unit
The engine control unit operates in line
with the torque.
The following information is supplied
over the CAN-BUS to the four-wheel
drive control unit:
– Engine speed
– Accelerator pedal position
– Engine torque
ABS control unit
SP29-66
SP29-67
failure
Engine does not run or
restricted engine running
(system-related)
In the very improbable
likelihood of total system
failure
– no 4x4 control
– only normal braking
operation without ABS
control
For further
function
descriptions see
SSP 12, SSP 19
SSP 28
The following information is supplied
over the CAN-BUS to the four-wheel
drive control unit:
– Wheel speeds
– Lateral acceleration
– Brake operation
On models fitted with ESP, the required
ESP control takes priority over the 4x4
function
30
Use of signal for 4x4 electronic control Effect in the event of signal
failure
Engine speed sender
For further
function
descriptions see
Actuation of charge pump (Haldex
coupling pump), which operates only
when ignition on and at an engine
speed of > 400 rpm.
Speed sensors of all 4 wheels
Detect change in speed of each
individual wheel and transmit wheel
speed information to the four-wheel
drive control unit. The factors detected
include cornering, manoeuvring mode,
acceleration phase, different tyre
circumferences.
SP29-68
SP29-69
Engine does not run or
engine running with
substitute values (systemrelated)
– no control of all-wheel
drive
– no ABS control
Failure of a speed sensor
does not yet result in any
restriction of four-wheel
drive.
For safety reasons, the
coupling is opened fully if no
speed signals are received.
SSP 19, SSP 27
SSP 26
Accelerator pedal position sender
SP29-70
Is used for transmitting driver request
to engine control unit and over the
CAN-BUS to the four-wheel drive
control unit. The torque at the Haldex
coupling is increased, for example, in
line with the particular driving
situation.
Emergency running
programme
SSP 27
31
Sensors
Hydraulic temperature sensor
The sensor is installed close to the control
valve in the housing of the four-wheel drive
control unit, and the hydraulic fluid flows
around it.
It is the only sensor which is provided
additionally specifically for the Haldex
coupling.
Use of signal
The sensor detects the current temperature
of the hydraulic fluid and supplies the
information to the four-wheel drive control
unit.
This information is used for adapting the
pressure control to the changing viscosity of
the hydraulic fluid.
Temperature
sensor
Temperature Hydraulic fluid/Viscosity Control valve
in negative range viscous opened a little further
normal 20˚C normal opened normally
more than 20˚C fluid opened slightly less
If the temperature of the hydraulic fluid rises
above 100˚C, the coupling is switched
pressureless. Once the temperature again
drops below 100˚C, pressure is again supplied
to the coupling.
Effect in the event of signal failure
All-wheel drive is switched off.
SP29-14
32
Longitudinal acceleration sensor
G249
It is located at the right A pillar and is required
only for all-wheel drive models with (ESP).
When the Haldex coupling is closed, the front
and rear wheels are rigidly coupled.
The real vehicle speed is calculated from the
signals supplied by the individual wheel
speed sensors and, in certain conditions, may
be too inaccurate if the friction coefficients are
low and the Haldex coupling is closed.
The measurement of the longitudinal
acceleration is used to backup the vehicle
speed which is calculated theoretically.
Effect in the event of signal failure
Without the additional measurement of the
longitudinal acceleration, it may not be
possible to accurately calculate the real
speed of the vehicle in certain unfavourable
conditions. The ESP and ASR functions then
do not operate.
SP29-18
If an ESP control cycle is activated, the Haldex
coupling is opened.
Electric circuit
The longitudinal acceleration sensor is linked
directly to the ABS control unit J104. The data
are transferred over the CAN-BUS.
G249
J104J492
CAN L
CAN H
SP29-17
G249 Longitudinal acceleration sensor
J104 ABS/EDL control unit
J492 Four-wheel drive control unit
33
Sensors
Handbrake indicator switch F9
The handbrake indicator switch is located
below the handbrake lever.
It operates as a normally-open contact.
Its main function is to operate the handbrake
indicator lamp K14.
Its signal is also used for information on
“handbrake operated” for controlling the allwheel drive.
Use of signal
The information “handbrake operated” flows
over the wiring loom directly to the four-wheel
drive control unit J492 and also to the ABS
control unit J104.
As soon as the direct signal is detected, the
positioning motor in the control valve is
operated by the four-wheel drive control
unit and the Haldex coupling is rendered
pressureless, in other words the coupling is
opened.
SP29-74
CAN L
CAN H
Effect in the event of signal failure
If no “handbrake operated” signal is received,
it is not possible in this case to control the allwheel drive.
If the signal is constantly present, e.g. because
the switch is faulty, the all-wheel drive is not
controlled.
J492
F9 K14
31 31
F9 Handbrake indicator switch
K14 Handbrake indicator lamp
J104 ABS/EDL control unit
J492 Four-wheel drive control unit
J104
SP29-16
34
Brake light switch F
Task
The brake light switch is located at the pedal
assembly.
It operates as a normally-open contact and its
main function is to switch on the brake lights.
The function is used at the same time for
supplying a signal to the ABS control unit
J104 and to the four-wheel drive control unit
J492.
Use of signal
SP29-75
The information “brake operated” flows over
the wiring loom to the ABS control unit.
This signal is also passed by the ABS control
unit over the CAN-BUS to the four-wheel drive
control unit.
When the signal is received, the four-wheel
drive control unit operates the positioning
motor in the control valve and the Haldex
coupling is rendered pressureless.
Effect in the event of signal failure
If no signal is received over the CAN-BUS, the
“brake operated” signal which is sent over the
additional direct link to the four-wheel drive
control unit is used in this case.
+
30
J492
S13
10A
F
J104
CAN L
CAN H
F Brake light switch
J104 ABS/EDL control unit
J492 Four-wheel drive control unit
SP29-15
35
Control Unit
Four-wheel drive control unit J492
The control unit is attached directly to the
housing of the Haldex coupling.
It forms a single unit together with the
positioning motor and the control valve.
The control unit is always switched on when
“ignition on”.
Design and function
The control unit is linked over the CAN
databus drive to the engine and ABS control
unit and over the vehicle wiring loom to other
sensors. It operates automatically, cannot be
switched off and analyses the following
signals which characterise the vehicle state,
and besides the pressure which should be
applied to the discs of the Haldex coupling.
– Accelerator pedal signal
(driver intention recognition)
– Engine speed
– Engine torque
– Wheel speeds, also when snow chains are
fitted to the front wheels
– EBD signal (whether electronic brake
pressure distribution is active)
– Brake operation
The oil pressure which is applied to the discs
of the Haldex coupling determines the torque
which is transmitted to the rear wheels.
Effect in the event of signal failure
SP29-72
No all-wheel drive.
Self-diagnosis
The control unit is incorporated in the selfdiagnosis of the vehicle.
36
Haldex coupling pump V181
The pump is installed in the housing of the
Haldex coupling.
It is an electrically driven internal gear pump
and operates as a pre-delivery pump for the
two pump pistons.
Design and function
Actuators
The pump operates only when the ignition is
switched on. As soon as the engine has
reached an idling speed of more than 400 rpm
after being started, voltage is applied to the
pump by the four-wheel drive control unit.
The two pump pistons of the coupling are
mounted floating.
The pump delivers oil to the pump pistons
and operates the pressure rollers to move the
pump pistons against the eccentric disc.
At the same time, pressurized oil flows to the
working piston.
The working piston is moved against the
multi-disc set by means of its pressure rollers.
As a result, the play is eliminated at the multidisc set which ensures rapid response. (The
eccentric disc runs empty if the ignition is off
and the Haldex coupling remains open.)
Effect in the event of signal failure
No all-wheel drive.
SP29-12
Haldex coupling
pump
Internal gear
of pump
SP29-11
D/15
V181
Electric circuit
The pump is supplied directly with voltage by
the four-wheel drive control unit.
J492 Four-wheel drive control unit
V181 Haldex coupling pump
31
S51
J492
M
31
SP29-10
37
Actuators
Oil pressure positioning motor V184
The positioning motor is integrated in the
housing of the four-wheel drive control unit. It
is part of the control valve, an electromotive
proportioning restrictor valve, with the aid of
which it is possible to adapt the torque
transmission capability.
Design and function
The positioning motor is supplied with
voltage by the four-wheel drive control unit.
It operates as a stepping motor.
When a command is received from the control
unit, the positioning motor alters the height of
the control pin in the control valve by means
of a pinion.
The height at which the control pin is
positioned in the control valve alters the cross
section of a return-flow drilling.
The pressure at the working piston of the
discs is determined in this way and the torque
transmission capability adapted accordingly.
Return-flow
drilling
Control pinPositioning
motor
Pinion
Control valve
Positioning
motor
SP29-63
Control valve closed:
Maximum pressure at the discs
Control valve partially opened:
Reduced pressure at the discs
Control valve fully opened:
No pressure at the discs.
38
SP29-73
Self-diagnosis
Self-diagnosis of the Haldex coupling
electrically monitors
– the signals of the sensors
– the operation of the actuators
– the control unit by means of a self-check.
If the control unit detects a fault or if CAN
messages are not received, it calculates a
substitute value from other signals and
provides an emergency running programme.
In the absence of vehicle speed signals, the
coupling is opened fully for safety reasons.
Self-Diagnosis
1
2
3
4
5
6
7
8
9
C
O
HELP
Q
V.A.G.
1552
Self-diagnosis can be carried out with
the vehicle system tester V.A.G 1552,
the fault reader V.A.G 1551, or
the vehicle diagnosis, measuring and
information system VAS 5051.
The address word is:
22 - All-wheel electronics
The following functions can be read:
01 -Interrogating control unit version
02 -Interrogating fault memory
03 -Final control diagnosis
04 -Basic setting
05 -Erasing fault memory
06 -Ending output
07 -Coding control unit
08 -Reading measured value block
All the faults set in the fault memory are read.
When faults are stored, the control unit
distinguishes between static and sporadic
faults.
If a fault occurs only once within several
driving cycles, it is stored as a sporadic fault.
202_CZ_002
SP17-29
02D 525 554 HALDEX LSC V00
Cod. ... WCC
If a fault no longer occurs after 50 driving
cycles (driving cycle = ignition on and vehicle
speed of at least 20 km/h), it is erased from the
fault memory.
If the fault is again present within the driving
cycles stored in the control unit, it is stored in
the control unit as a static fault.
39
Function Diagram
S15
5A
+
30
S51
5A
+
30
+
30
D
S13
10A
G249
F
J... J104
V181
M
31
CAN L
CAN H
V184 G271
M
J492
F9
K14
J218
K
31
SP29-01
40
The function diagram represents a simplified
current flow diagram.
It shows the linkages of the system
components for controlling the all-wheel
drive.
Legend of function diagram
Components
D Ignition/starter switch
F Brake light switch
F9 Handbrake indicator switch
G249 Longitudinal acceleration sensor*
G271 Hydraulic temperature sensor
J … Engine control unit
J104 ABS/EDL control unit
J218 Combination processor in dash
panel insert
J492 Four-wheel drive control unit
K Diagnostic connection
K14 Handbrake indicator light
V181 Haldex coupling pump
V184 Oil pressure positioning motor
S Fuse
Colour coding/Legend
= Input signal
= Output signal
= Battery positive
= Earth
= Bi-directional
in out
* only on models with ESP
41
Driving Situations
A feature of the permanent all-wheel drive
with Haldex coupling is that it operates
without any action on the part of the driver,
but controls the necessary stiffness of the
coupling in line with the driving situation
detected.
Driving situation
Parking Acceleration Fast driving
Difference in speed between front axle
and rear axle
slight high low
The overview below helps us to rapidly
recognize the operating principle of the
Haldex coupling in particular driving
situations.
SP29-55 SP29-56 SP29-57
Torque required at rear axle low high low
Status of multi-disc coupling slight contact
Input signals – engine torque
Note:
In the event of a failure of peripheral
systems (ABS, sensors, CAN-BUS) the
Haldex coupling switches to an
emergency programme which
permits
pressure
– engine speed
– accelerator pedal
position
– 4 x wheel sensors
limited torques to be transmitted
without affecting safety and
manoeuvrability.
High contact
pressure, up to as
much as maximum,
EDL control may
increase the contact
pressure
– engine torque
– engine speed
– accelerator pedal
position
– 4 x wheel sensors
closed, as required
– engine torque
– engine speed
– accelerator pedal
position
– 4 x wheel sensors
42
Driving on
slippery surface
Driving with
tyres with different
rolling radii
SP29-60 SP29-61 SP29-62SP29-59SP29-58
Braking (ABS or
ESP operation)
Towing Brake test (roller
dynamometer)
varies between low
and high
varies between low
and high
closed, up to
maximum
normal to high normal to high high high
low 0 0 0
open or slightly
closed
– engine torque
– engine speed
– accelerator pedal
position
– 4 x wheel sensors
– CAN data transfer
– 4 x wheel sensors
– through ABS
control unit
open open, electric pre-
pressure pump off
(if ignition off)
– 4 x wheel sensors
– to ABS control
unit
– brake light switch
none none
open, electric prepressure pump off
(if ignition off)
Note:
The Haldex coupling also operates
when reversing!
43
Test Your Knowledge
Which answers are correct?
Sometimes only one.
But perhaps also more than one - or all!
1. The Haldex coupling operates on the basis of three main
elements. These are:
A. Mechanical system
B. Pneumatic system
C. Electronic system
D. Hydraulic system
2. The all-wheel drive with Haldex coupling is particularly characterised by:
A. Permanent all-wheel drive with electronically controlled multi-disc coupling.
B. Acceleration with good directional stability (front-wheel drive characteristic).
C. Delayed response.
3. The pump for the Haldex coupling is operated electrically once the engine speed is:
A. higher than 400 rpm
B. less than 400 rpm
4. The pressure rollers of the pump pistons pass through a peak and valley track on the
eccentric disc if a speed difference between the front wheels and the rear wheels.
The pump pistons pulsate and build up a pressure.
Which of the following statements are correct?
?
A. The pressure flows through the pressure valves to the working piston and through
its pressure rollers to the multi-disc coupling.
B. The pressure is limited by the pressure limiting valve.
C. The pressure is influenced by the control valve.
5. The accumulator
A. determines the maximum pressure.
B. determines the pre-pressure of 0.4 MPa (4 bar).
C. acts as a damper in order to smooth out pressure variations.
?
44
6. The positioning motor is supplied with voltage by the four-wheel drive control unit and
operates the control pinion in the control valve by means of a pinion. As a result, the
return-flow drilling is more or less closed.
Which of the following statements is correct?
A. Return-flow drilling in control valve closed = no pressure at the discs
B. Return-flow drilling in control valve open = maximum pressure at the discs
C. Return-flow drilling in control valve open = no pressure at the discs
D. Return-flow drilling in control valve closed = maximum pressure at the discs
7. Which sensor signals are supplied direct to the four-wheel drive control unit?
A. Longitudinal acceleration sensor
B. Handbrake switch
C. Brake light switch
D. Hydraulic temperature sensor
8. The hydraulic temperature sensor is installed in the housing of the four-wheel drive
control unit. It detects the current hydraulic fluid temperature.
What is this information used for in the control unit?
A. For adapting to the changing viscosity of the hydraulic fluid by means of the
pressure controller.
B. For emergency running.
C. For rendering the coupling pressureless if a temperature of 100˚C is reached.
9. If a major speed difference exists between the front and rear wheels, for example when
accelerating:
A. the torque which has to be transmitted to the rear axle is ..............................
B. the contact pressure at the multi-disc coupling is ..............................
The following input signals are of significance:
C. ....................... D. ....................... E. ....................... F. .......................
?
45
46
Answers
1. A., C., D.; 2. A., B.; 3. A.; 4. A., B., C.; 5. B., C.; 6. C., D.; 7. B., C., D.; 8. A., C.;
9. A = high, B = high, C = Engine torque, D = Engine speed, E = Accelerator pedal position,
F = 4 x wheel sensors
47
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