Audi_TT_Haldex_SelfStudyGuide.pdf

Haldex Coupling

The development of the Haldex coupling is a

giant step forward in modern all-wheel-drive

technology. The Haldex coupling is control-

lable, based on the inputs the Haldex control

module receives from the vehicle.

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), the

electronic differential lock (EDL), the anti-

slip regulation (ASR), the electronic brake

distribution system (EBD) and electronic

stabilization program (ESP)

Slip is no longer the only decisive factor in

the distribution of drive forces; the car's

dynamic state is also a factor. The Haldex

control module monitors the ABS wheel

speed sensors and the engine control mod-

ule (accelerator pedal signal) via the CAN

bus. This data provides the control module

with all the information it needs on road

speed, cornering, coasting or traction mode,

and can respond optimally to any driving sit-

uation.

Haldex Coupling

Haldex Coupling

The Haldex coupling is mounted on the rear

axle differential and is driven by the prop

shaft.

Engine torque is transmitted to the prop

shaft through the gearbox, the front axle dif-

ferential and the front axle drive.

Rear Differential

Haldex Coupling

The prop shaft is connected to the input

shaft of the Haldex coupling. In the Haldex

coupling, the input shaft is separated from

the output shaft to the rear axle differential.

Torque can only be transmitted to the rear

axle differential when the Haldex coupling

clutch plates are engaged.

Prop Shaft

Rear Differential

Engine and Transmission

Haldex Coupling

Prop Shaft

Haldex Coupling

Haldex System

The parts include:

The electronics are:

• the input shaft

• the inner and outer clutch plates

• the lifting plate

• the roller bearing with annular piston

• the output shaft

• the pump for Haldex coupling

• the regulating valve positioning motor

• the temperature sensor

• the Haldex control module

The hydraulics are:

The Haldex oil and oil filter must

be replaced every 20,000 miles

(32,000 km). Refer to AESIS for

the latest maintenance sched-

ules and service procedures

• the pressure valves

• the accumulator

• the oil filter

• the annular piston

• the regulating valve

Lifting Plate

Pressure Limiting Valve

Clutch Plates

Accumulator

Output Shaft

Oil Filter

Input Shaft

Annular Piston

Control Module

Electric Pump

Regulating Valve

Positioning Motor

Temperature

Sensor

Regulating Valve

Haldex Coupling

The Multi-plate Clutch

The clutch input shaft, indicated in blue in

the figure, is connected to the prop shaft.

The roller bearings for the lifting piston and

the working piston, as well as the outer

clutch plates, are engaged when the input

shaft rotates.

The lifting and working pistons are annular

pistons. The output shaft, indicated in red in

the figure, forms a unit from the lifting plate

through to the drive pinion head. The inner

clutch plates are also connected to the out-

put shaft via longitudinal toothing.

Outer Clutch Plate

Roller Bearing for

Working Piston

Inner Clutch Plate

Working Piston

Output Shaft

Roller Bearing for

Lifting Piston

Lifting

Piston

Drive Pinion Head

Input Shaft

Lifting Plate

Disengaged Haldex Clutch Assembly

Haldex Coupling

Function

When a speed difference is present

between the input and output shafts, the

input shaft, together with the roller bearing

of the lifting piston, rotates around the still

stationary lifting plate of the output shaft.

This oil pressure is diverted via an oil duct to

the working piston. The oil pressure forces

the working piston to move to the left

against the bearing roller and the pressure

plate of the clutch plate set.

The roller bearing of the lifting piston tracks

along the undulating surface of the lifting

plate. The roller transfers these upward and

downward movements to the lifting piston.

The clutch plate set is compressed.

The input shaft and the output shaft of the

clutch are now interconnected, connecting

both the front and rear axles and making all-

wheel drive possible.

This causes the lifting piston to perform a lift

movement, building up oil pressure.

Clutch Plate Set

Pressure Plate

Oil Duct

Output Shaft

Input Shaft

Lifting Plate

Engaged Haldex Clutch Assembly

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