12

Haldex Coupling

The development of the Haldex coupling is agiant step forward in modern all-wheel-drivetechnology. The Haldex coupling is control-lable, based on the inputs the Haldex controlmodule receives from the vehicle.

Slip is no longer the only decisive factor inthe distribution of drive forces; the car'sdynamic state is also a factor. The Haldexcontrol module monitors the ABS wheelspeed sensors and the engine control mod-ule (accelerator pedal signal) via the CANbus. This data provides the control modulewith all the information it needs on roadspeed, cornering, coasting or traction mode,and can respond optimally to any driving sit-uation.

Characteristics of the Haldex coupling:

• Permanent all-wheel drive with electroni-cally controlled multi-plate clutch

• Front drive characteristic• Quick response• No strain on clutch when parking and

maneuvering vehicle• Compatible with different tires (e.g.

emergency wheel)• No restrictions on towing with the rear

axle on the ground• Fully combinable with systems such as

the anti-lock brake system (ABS), theelectronic differential lock (EDL), the anti-slip regulation (ASR), the electronic brakedistribution system (EBD) and electronicstabilization program (ESP)

Haldex Coupling

13

Haldex Coupling

The Haldex coupling is mounted on the rearaxle differential and is driven by the propshaft.

Engine torque is transmitted to the propshaft through the gearbox, the front axle dif-ferential and the front axle drive.

The prop shaft is connected to the inputshaft of the Haldex coupling. In the Haldexcoupling, the input shaft is separated fromthe output shaft to the rear axle differential.

Torque can only be transmitted to the rearaxle differential when the Haldex couplingclutch plates are engaged.

Prop Shaft

Rear Differential

Haldex Coupling

Haldex Coupling

Prop Shaft

Engine and Transmission

Rear Differential

14

Haldex System

The parts include:

• the input shaft• the inner and outer clutch plates• the lifting plate• the roller bearing with annular piston• the output shaft

The electronics are:

• the pump for Haldex coupling• the regulating valve positioning motor• the temperature sensor• the Haldex control module

The hydraulics are:

• the pressure valves• the accumulator• the oil filter• the annular piston• the regulating valve

Haldex Coupling

Input Shaft

Pressure Limiting Valve

Oil Filter

Control Module

Regulating Valve

Positioning MotorTemperature

Sensor

Electric Pump

Lifting Plate

Clutch Plates

Output Shaft

Annular Piston

Accumulator

Regulating Valve

The Haldex oil and oil filter mustbe replaced every 20,000 miles(32,000 km). Refer to AESIS forthe latest maintenance sched-ules and service procedures

15

The Multi-plate Clutch

The clutch input shaft, indicated in blue inthe figure, is connected to the prop shaft.The roller bearings for the lifting piston andthe working piston, as well as the outerclutch plates, are engaged when the inputshaft rotates.

The lifting and working pistons are annularpistons. The output shaft, indicated in red inthe figure, forms a unit from the lifting platethrough to the drive pinion head. The innerclutch plates are also connected to the out-put shaft via longitudinal toothing.

Haldex Coupling

Disengaged Haldex Clutch Assembly

Input Shaft

Working Piston

Inner Clutch Plate

Roller Bearing for

Working Piston

Drive Pinion Head

Lifting Plate

Outer Clutch Plate

Output Shaft

Lifting

Piston

Roller Bearing for

Lifting Piston

16

This oil pressure is diverted via an oil duct tothe working piston. The oil pressure forcesthe working piston to move to the leftagainst the bearing roller and the pressureplate of the clutch plate set.

The clutch plate set is compressed.

The input shaft and the output shaft of theclutch are now interconnected, connectingboth the front and rear axles and making all-wheel drive possible.

Function

When a speed difference is presentbetween the input and output shafts, theinput shaft, together with the roller bearingof the lifting piston, rotates around the stillstationary lifting plate of the output shaft.

The roller bearing of the lifting piston tracksalong the undulating surface of the liftingplate. The roller transfers these upward anddownward movements to the lifting piston.

This causes the lifting piston to perform a liftmovement, building up oil pressure.

Haldex Coupling

Engaged Haldex Clutch Assembly

Input Shaft

Clutch Plate Set

Oil Duct

Lifting Plate

Pressure Plate

Output Shaft

17

When a difference in speeds occursbetween the front and rear axles, the outerclutch plate housing, together with the rollerbearings, rotates around the output shaft insuch a way that the roller bearings of the lift-ing piston roll on the lifting plate.

Due to the shape of the lifting plate, theroller bearings of the lifting piston follow anundulating path and transfer the lifting move-ment to the lifting pistons in the housing.

The output shaft, with its splines for theinner clutch plate, combines with the liftingplate and the drive pinion head to form aunit.

Haldex Coupling

The roller bearings are shownhere for your information only.

For reasons of clarity, we haveshown the lifting plate withtwo cams. In reality, however,there are three cams on thelifting plate. The functionremains unchanged.

Engaged Haldex Clutch Assembly

Lifting Plate

Roller Bearing for

Working Piston

Inner Clutch Plate

Drive Pinion Head

Roller Bearing for

Lifting Piston

18

The outer clutch plate housing, together withthe splines for the outer clutch plate and theroller bearing form, combines with the inputshaft to form a unit.

The lifting movement of the lifting piston pro-duces an oil pressure which acts on theworking piston via the oil duct and pushesthe piston to the left.

The pressure is transferred via a pressureplate to the clutch plate set via the rollerbearings of the working piston. The clutchcloses and thus interconnects the front andrear axles.

Haldex Coupling

The roller bearings are locatedin the outer clutch plate hous-ing, as shown here.

The roller bearings are shownhere for your information only.

Outer Clutch Plate Housing

Clutch Housing

Oil Duct

Lifting Piston

Working Piston

Input Shaft

Splines

19

Diagram of Oil Pressure System

The pressure limiting valve determines themaximum pressure on the clutch plates.

You have already seen how oil pressure isbuilt up at the lifting piston as a result of adifference in speeds between the input shaft(blue) and the output shaft with lifting plate(red).

This oil pressure is regulated by valves. Theplate clutch can thus allow a certain amountof slip when open and nearly closed.

Haldex Coupling

For reasons of clarity, we explained the function on the previous pages using alifting piston by way of an example. In reality, there are two lifting pistons in theclutch housing; these pistons are actuated by roller bearing pairs. Therefore, twosuction valves and two pressure valves are also required.

Lifting Plate Pressure Valves

Bearing

Clutch

Plate Set

Working

Piston

Lifting

Piston

Pump

Suction

Valves

Filter

Pump

Strainer

Accumulator

Positioning

Motor

Regulating

Valve

Pressure

Limiting

ValveRoller

Bearing

Pair

20

Haldex Coupling

Engine Speed Sensor

G28

Acceleration Position

Sensor G79/G185

Wheel Speed Sensors

G44-G47

Longitudinal

Acceleration Sensor

G249

Brake Light Switch F

Handbrake Switch F9

Motronic Engine Control

Module J220

ABS Control Module J104

21

Haldex Coupling

Handbrake Switch F9

Temperature Sender G271

Haldex Control

Unit J492

Positioning

Motor V184,

controls

regulating

valve Haldex Clutch

Pump V181

Diagnosis Plug

Connection

22

Signal utilization for the all-wheel drive

electronics

The Motronic ECM provides the followingsignals to the Haldex control module alongthe CAN bus:

• Engine speed signal• Accelerator pedal position• Engine torque

Effects of signal failure:

• The Haldex unit will not operate

The Motronic Engine Control Module

The Motronic engine control module (ECM)is mounted in different areas on the variousvehicles, but is normally accommodated inthe plenum chamber. The operating mode ofthe Motronic ECM is torque-oriented.

Haldex Coupling

Motronic Engine Control Module J220

23

Electrical circuit

Engine Speed Sensor G28

The engine speed sensor is an inductivesensor and is installed near the the oil filteron the left-hand side of the engine.

Signal utilization

The sensor records the exact angular posi-tion of the crankshaft to determine the igni-tion and injection point, as well as enginespeed.

Engine speed

As soon as the engine turns, the sensorwheel moves past G28 and generates analternating current (AC) voltage. The fre-quency and amplitude of this voltagechanges with engine speed.

The Motronic ECM calculates the enginespeed from the frequency of the AC voltage.

Ignition point

For recognizing the crankshaft position, thewheel has a larger gap trigger tooth whichserves as a reference mark.

Effects of signal failure

If the engine speed signal supplied by theengine speed sensor fails, the engine willnot be started or run.

If no engine speed signal is received, theHaldex control module will not energize thepump, leaving the rear axle drive capabilitydisabled. This also allows the vehicle to betowed with the rear wheels on the ground.No power will be transmitted back throughthe wheels to the transmission.

Haldex Coupling

Sender Wheel

Engine Speed

Sensor G28

J220

G28

24

Throttle Position Sensor G79/G185

The throttle position sensor sends an analogsignal corresponding to the accelerator pedalposition to the Motronic ECM. Two indepen-dent potentiometers, G79 and G185, makeup the throttle position sensor.

The Haldex control module uses this signalin combination with other signals to deter-mine when and how much power should beapplied to the rear axle. The throttle positionsensor represents the driver intention, and isnot necessarily how the Motronic ECM isallowing the engine to operate.

Effects of signal failure

The Motronic ECM monitors G79 and G185for proper functioning and plausibility. If oneof the two sensors fails, the other sensoracts as a back-up. The warning lamp K132on the instrument panel will illuminate andthe vehicle will enter emergency runningmode.

If this signal is not available to the Haldexcontrol module, all-wheel drive will not beavailable.

Haldex Coupling

Throttle Pedal Position Sensor G79/G185

25

If the vehicle also has the elec-tronic stabilization program(ESP), then ESP control takesprecedence over the all-wheeldrive function.

ABS Control Module J104

The anti-lock brake system (ABS) controlmodule (by ITT Automotive) is combinedwith the hydraulic unit as a module andmounted in the engine compartment on theleft-hand side.

When the ignition is turned on, the controlmodules carry out a self-test. The controlmodule consists of two processor systems.This ensures a high level of fail-safety. Inaddition to monitoring individual compo-nents, the two processor systems monitoreach other.

Signal utilization for all-wheel-drive elec-

tronics

The following signals are supplied to theHaldex control module along the CAN bus:

• Wheel speed sensor• Brake light switch• Handbrake switch• Longitudinal acceleration sensor

Effects of signal failure

In the unlikely event of total failure of thecontrol module, the Haldex unit will not func-tion properly.

Haldex Coupling

ABS Control Unit

Hydraulic Brake Unit

26

Wheel speed sensors G44 - G47

The wheel speed sensor detects the changein speed of the wheel and sends this infor-mation to the ABS control module in theform of wheel speed information. This infor-mation is then sent to the Haldex controlmodule via CAN-bus.

The wheel speed sensor is mounted in thevicinity of the axle flange. A toothed wheelis positioned on the axle flange in such away that it moves past the top end of thewheel speed sensor when the wheelrotates.

Magnetic lines of force between the toothand tooth gap of the toothed wheel are dis-torted. This induces a sine-wave AC voltagein the coil of the engine speed sensor.

The frequency and amplitude in the coil isdependent on the wheel speed. The ABScontrol module calculates the momentaryspeed of individual wheels from the frequen-cy.

Effects of signal failure

• No ABS control• No four-wheel-drive control

Haldex Coupling

Toothed Wheel Speed Sensor

Wheel Speed Sensor

27

Longitudinal Acceleration Sensor G249

The longitudinal acceleration sensor G249 isattached to the right side A pillar.

On vehicles that are driven at one axle only,the system calculates the vehicle’s longitudi-nal acceleration from the data supplied bythe Sensor -2- for Brake Pressure G214, thesignals supplied by the ABS wheel speedsensors and information from the enginemanagement system.

On four-wheel drive vehicles with the Haldexcoupling, the front and rear wheels are con-nected when the coupling is closed. The cal-culated true vehicle road speed, which isdetermined from the individual wheelspeeds, may be too inaccurate under certainconditions at low coefficients of friction andwhen the Haldex coupling is closed. Thelongitudinal acceleration measured is used toverify calculated road speed.

Effects of signal failure

Without the additional measurement of lon-gitudinal acceleration, it is not possible todetermine the true vehicle road speed exact-ly in unfavorable conditions. As a result, theelectronic stability program (ESP) and anti-slip regulation system (ASR) will not operate.

Haldex Coupling

Electrical circuit

The longitudinal acceleration senor is con-nected to the control unit J104 via threelines.

Longitudinal Acceleration Sensor

28

Effect of signal failure

The information provided by the CAN bus isused as an alternative.

Brake Light Switch F

Brake light switch F is located at the upperend of the brake pedal and is secured to thepedal support.

Signal utilization

The brake light switch sends the "brake acti-vated" signal to ABS control module J104.The control unit informs the Haldex controlmodule along the CAN bus.

When the brake is applied, the Haldex con-trol module immediately opens the pressureregulator via the positioning motor and theHaldex coupling clutch is opened.

Electrical circuit

Haldex Coupling

Brake Light Switch

29

Effects of signal failure

If the switch remains closed, then no all-wheel drive control is available and restric-tions are placed on ABS control.

Handbrake Switch F9

Handbrake switch F9 is located under thehand brake lever.

Signal utilization

The handbrake switch sends the "handbrakeengaged" signal to the ABS control moduleJ104 and simultaneously to the Haldex con-trol module J492.

Whereas the ABS control module transfersthis information to the Haldex control unit in"filtered" form along the CAN bus, theHaldex control module also receives theinformation directly from the handbrakeswitch.

If the signal generated by handbrake switchF9 is picked up, the Haldex coupling clutch isopened.

Electrical circuit

Haldex Coupling

Handbrake Switch F9

30

Haldex Coupling Temperature Sensor

G271

The Haldex coupling temperature sensor isinstalled near the regulating valve in theHaldex control module housing and isimmersed in hydraulic fluid.

Signal utilization

The temperature sensor senses the momen-tary hydraulic oil temperature and sends thisinformation to the Haldex control module.This information is used for adapting to thechanging viscosity of the hydraulic fluid.

If the hydraulic fluid temperature exceeds100°C, the clutch is released. If the tempera-ture of the hydraulic fluid drops below100°C, the clutch is again pressurized.

Effects of signal failure

All-wheel drive is shut off if no signal isreceived from the temperature sensor G271.

Haldex Coupling

Temperature Hydraulic Fluid/Viscosity Regulating Valve

In the minus range High viscosity Slightly more open

Normally 20º C Normal Normally open

Over 20º C Low viscosity Slightly less open

Temperature Sensor

31

Effects of signal failure

If the Haldex control module is not operatingcorrectly, no all-wheel drive is possible.

Haldex Control Module J492

The Haldex control module is mounteddirectly on the housing of the Haldex cou-pling and combines with the positioningmotor and the regulating valve to form aunit.

Design and function

The Haldex coupling control module is con-nected to the engine and the ABS controlunit via the CAN bus. From the signals thatare generated by the Motronic ECM sen-sors, the Haldex control module decideswhat oil pressure to apply to the plates ofthe Haldex coupling clutch.

The oil pressure acting on the plates of theHaldex coupling clutch determine whattorque is to be transmitted to the rear axle.

Haldex Coupling

Haldex Control Module J492

The address word to access theHaldex Control Module is 22.

32

Positioning Motor V184

The positioning motor is integrated in theHaldex control module housing.

Design and function

The positioning motor is supplied with volt-age by the Haldex control module and func-tions as a stepping motor.

At the command of the Haldex control mod-ule, the positioning motor changes the levelof the regulating pin in the pressure regula-tor via a small pinion gear.

The level of the regulating pin changes thecross section of a return bore in the pres-sure regulator. This controls the pressureacting on the working piston, and in turn, onthe clutch plates.

Haldex Coupling

Return

Bore

Regulating

Valve

Regulating

Pin

Pinion

Positioning

Motor

Positioning

Motor

Regulator Closed:

Maximum pressure on clutchplates.

Regulator Partially Open:

Reduced pressure on clutchplates.

Regulator Fully Open:

No pressure on clutch plates.

33

Haldex Clutch Pump V181

The pump for the Haldex coupling isattached to the Haldex coupling housing.

Electrical circuit

Design

After the engine has been started, the pumpfor the Haldex coupling is supplied with volt-age by the Haldex control module as soon asthe engine speed exceeds 400 rpm.

Function

The pump for the Haldex clutch conveys oilto the lifting piston and brings the lifting pis-ton into contact with the lifting plate viaroller bearings.

At the same time, oil reaches the workingpiston. This eliminates any play from theclutch plate set and ensures quick clutchresponse.

Effects of signal failure

No all-wheel drive.

Haldex Coupling

The Haldex clutch pump isdirectly supplied with voltageby the Haldex control module.

Haldex Clutch Pump

34

Haldex Coupling

Difference in speed between front

and rear axles

Torque required at the rear axle

Condition of multi-plate clutch

Input Signals

Parking

Low

Low

Low contact pressure

• Engine torque• Engine speed• Accelerator

pedal position• Four wheel

sensors

Acceleration

High

High

High contact pres-sure, up to maximum.EDL control systemcan increase contactpressure.

• Engine torque• Engine speed• Accelerator pedal

position• Four wheel sensors

High-speed Driving

Low

Low

Closed, as required

• Engine torque• Engine speed• Accelerator pedal

position• Four wheel sensors

35

Haldex Coupling

Slippery Surfaces

Fluctuates betweenlow and high

Fluctuates betweenlow and high

Closed, up to maxi-mum

• Engine torque• Engine speed• Accelerator pedal

position• Four wheel sensors• CAN-bus

communication

Emergency wheel

installed

Normal to high

Low

Open or slightlyclosed

• Four wheelsensors

• via ABS controlunit

Braking

Normal to high

0

Open

• Four wheelsensors

• via ABS controlunit

• Brake light switch

Towing

High

0

Open, electrical pre-pressure pump is offwhen ignition is off

• Engine speed lessthan 400 rpm

36

Components

D Ignition switch

F Brake light switch

F9 Hand brake warning switch

G271 Hydraulic temperature sensor

J220 Motronic engine control module

J104 ABS control module with EDL/TCS/ESP in the engine compartment at the left

J285 Control module with display unit in the dash panel insert

J492 Control module for four-wheel drive (located near the rear axle differential)

K Connection(K-wire (diagnosis)

K14 Handbrake warning lamp

M21 Bulb for left rear brake

S51 Fuse

V181 Haldex clutch pump

V184 Positioning motor for oil pressure

A80 Connection -1- (x) in dash panel wiring harness

A121 Connection (Hi bus)

A122 Connection (Low bus)

Haldex Coupling

Input signal

Output signal

Positive

CAN

Ground

37

Haldex Coupling

38

Self-diagnosis

The self-diagnosis electrically monitors:

• the signals generated by the sensors• activation of the positioning motors• the control unit by carrying out a self-test

If the control unit detects a fault, it calcu-lates a substitute value from other signalsand makes an emergency running programavailable.

In the data transfer facility, the followingfunctions can be read out under the addressword 22 "4-wheel-drive electronics" with theVAS 5051 testing and information system:

02 Check DTC Memory

03 Output Diagnostic Test Mode (DTM)

05 Erase DTC Memory

06 End Output

08 Read Measuring Value Block

For more detailed information, please referto AESIS.

Haldex Coupling

VAS 5051 Scan Tool