Get Power transmission -> Two-speed transmission 0ME Guide for Audi RS E Tron Gt 4 Door First Generation (2021-2026)

Two-speed transmission 0ME

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The Audi e-tron GT (type F8) is fitted with two-speed transmission unit 0ME on the rear axle as standard equipment. The transmis-

sion unit is fitted parallel to the axle and has two continuous speed reduction stages and one planetary gear set. The transmission

unit has the factory designation EQ550-2P.

An active differential lock is available as optional equipment for the Audi e-tron GT. This active differential lock is standard equip-

ment on the Audi RS e-tron GT.

44

Reference

You can view the components of two-speed transmission unit – 0ME in detail using the AR application AR "Audi e-tron

GT (Type F8) - Drive / Power Transmission".

Three selector elements - a freewheel, a dog clutch and a multi-plate clutch- enable the transmission unit to perform the following

tasks:

›

Shifting between 1st and 2nd gear. The different ratios are achieved using a planetary gear set.

Reversing in transmission position R. This is done by reversing the direction of rotation on the electric drive motor in 1st gear

and engaging the dog clutch for power transmission.

›

Activating the parking lock function. This is done by blocking the gears and locking them in position.

Enabling neutral position.

The shift matrix shows the interaction between the selector elements required for the transmission functions.

Transmission position/gear

Ratio

1 (R/N)

2

15,560

8,160

Transmission position D is the only position available for driving forwards. The gear selection can be influenced using the Audi drive

select modes efficiency, comfort and dynamic.

Exploded view

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The multi-plate clutch and dog clutch are operated via the selector fork and the release fork, which are controlled by the shift

drum.

The shift drum is actuated by gear actuator VX65 via a spur gear drive.

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The two fixed-ratio gear sets 1 and 2 are always involved in the power transmission and yield a constant ratio of 8.16 : 1. This ratio

corresponds to that of 2nd gear, as here the planetary gear set is blocked, and therefore rotates without speed transformation (i.e.

1 : 1).

For 1st gear and reverse gear, the planetary gear ratio of 1.907 is applied. Together, the two gear ratios (8.16 x 1.907) yield a ratio

of 15.56 : 1.

There is no physical neutral position in the transmission unit. This means that the electric drive motor is always engaged for power

transmission to the wheels.

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Freewheel

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The freewheel is one of the three selector elements of two-speed transmission 0ME. It provides the basis for 1st gear, for shifting

from 2nd gear back to 1st gear, and for the parking lock function. Its task as a component is to block the sun gear from turning in

one direction, and to ensure free rotation in the other direction (i.e. of freewheel rotation).

The rotor of the freewheel interlocks with a shaft journal connecting it to the sun gear. The stator of the freewheel has a flange

with dog teeth that allow it to be mounted for co-rotation in the transmission unit housing.

On the end of the rotor of the freewheel are teeth for the dog clutch. When the dog clutch is engaged, these teeth interlock with

the teeth on the stator of the dog clutch and block the sun gear in the direction of freewheel rotation.

This means that the sun gear is blocked in both directions when the dog clutch is engaged.

The shift matrix shows the interactions between the selector elements that are required for the transmission functions.

Note

The term “freewheel” has two meanings:

›

A component that blocks the rotation of a shaft in one direction (locking direction) and allows the shaft to turn free-

ly in the other direction.

A state in which kinetic energy allows the vehicle to roll along freely. This is also referred to as coasting.

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Dog clutch

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The dog clutch is one of the three selector elements of two-speed transmission 0ME. It is required for reverse gear, recuperation in

1st gear, and the parking lock function.

When the dog clutch is engaged, it blocks the rotor in the direction of freewheel rotation.

As the rotor interlocks with a shaft journal connecting it to the sun gear, the sun gear is blocked in both directions of rotation when

the dog clutch is engaged:

›

In one direction of rotation by the freewheel

In the other direction of rotation by the dog clutch

The stator of the dog clutch is mounted for co-rotation in the transmission housing via the dog teeth on the stator. It is engaged

and disengaged by a selector fork that moves it along a shaft in the transmission unit housing. When engaging the clutch, the se-

lector fork slides the stator towards the rotor, and the dog teeth on the side of the stator mesh with the dog teeth on the rotor.

The shift matrix shows the interactions between the selector elements that are required for the transmission functions.

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Actuation of the dog clutch

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When the shift drum rotates, the guide pin engaged in the guide slot causes the selector fork to extend.

This causes the stator to be moved back and forth via the two spring-loaded joints connecting it to the selector fork.

When the dog clutch engages, the stator is moved towards the rotor. The spring-loaded joint ensures that the selector fork does

not block when the dog teeth are aligned tooth on tooth. If this happens, it causes the dog teeth to be pre-loaded and to engage,

and the dog clutch engages as soon as the rotor turns.

Motor control unit J623 detects the “tooth on tooth” position via clutch jaw position sensor G1016. In order to engage the dog

clutch, the electric drive motor is actuated minimally, if necessary, so that the rotor turns far enough for the dog teeth to engage,

and sensor G1016 detects a fully engaged dog clutch.

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Dog clutch, disengaged

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Key:

Dog clutch engaging/engaged

Dog clutch disengaging/disengaged

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Points to note regarding how the dog clutch is operated

Dog clutch aligned tooth on tooth

Dog clutch engaged

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The freewheel exhibits a certain degree of elasticity when subjected to torque in the direction of rotation in which it blocks. The

greater the torque the freewheel is subjected to, the more it rotates slightly in the direction in which it blocks. This causes the rotor

of the dog clutch to rotate as well.

This effect is exhibited in situations such as:

›

Powerful acceleration in 1st gear

Parking on an incline when the parking lock function is activated and the parking brake is not engaged

If this happens, the dog clutch may engage when there is minimal overlap in the “tooth on tooth” position due to the rotation of

the freewheel under high torque. In this situation, there is a risk that the freewheel springs back when the torque eases off, caus-

ing the dog clutch to be pre-tensioned in such a way that it cannot be disengaged again.

If the dog clutch cannot be released, it is not possible to shift up from 1st into 2nd gear.

To prevent the situation described here, the dog clutch is prevented from engaging when shifting from 2nd gear back into 1st gear

at high loads. In this case, the shift drum remains in shift state C (dog clutch still disengaged), (refer to image “684_337”). As

recuperation in 1st gear requires the dog clutch to be engaged, recuperation is not possible at this stage.

The dog clutch is not engaged until the operating conditions are no longer critical.

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Multi-plate clutch

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Two-speed transmission 0ME is equipped with a multi-plate clutch that is closed by a diaphragm spring when the clutch is not op-

erated.

When the multi-plate clutch is closed, it connects the planet carrier with the annulus. As a result, the planetary gear set is blocked

and co-rotates as a unit. No speed reduction takes place in the planetary gear set.

This shift state is required for 2nd gear and for the parking lock function.

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Disengaging/engaging the clutch

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The shift drum actuators are responsible for disengaging/engaging the multi-plate clutch.

An angled guide on the shift drum actuates the release fork for the multi-plate clutch via a roller with needle bearings. The release

fork actuates the release bearing to disengage and engage the multi-plate clutch.

When the multi-plate clutch is disengaged, the planetary gear set is no longer blocked.

The planetary gear set therefore serves as a speed reduction stage for 1st gear and reverse gear.

The multi-plate clutch is open when transmission position N is activated. This makes it possible to push the vehicle even if the dog

clutch and freewheel are engaged.

The movement of the release fork is registered by clutch position sender G476.

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Shift drum actuation

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The dog clutch and the multi-plate clutch are actuated via the shift drum.

For this purpose, the shift drum has a guide groove for the selector fork of the dog clutch, and an angled guide for the release fork

of the multi-plate clutch.

Gear actuator VX65 actuates the shift drum via a two-stage reduction gearing. This enables the gear actuator motor to apply the

amount of force required for actuation.

Motor control unit J623 determines the appropriate gear based on the current operating status and activates gear actuator VX65

via a sub-bus system (motor control unit CAN bus).

Shift drum locking mechanism

When the vehicle is moving, it must not be possible for the parking lock function to be activated. There is a locking gate on the face

of the toothed wheel for the shift drum for this purpose, (refer to image “684_372”). When the vehicle is driven, the locking pin of

parking lock solenoid N486 protrudes into the locking gate and prevents the shift drum from turning to shift state A (P-ON).

If the vehicle comes to a halt, current flows to solenoid N486, which causes the locking pin to be pulled out of the slot. Now the

shift drum can turn to shift state A (P-ON); the parking lock is then engaged.

Voltage is induced in the coil when the locking pin is pulled out of the slot. This voltage signal is evaluated as feedback and provides

assurance that the locking pin has been removed from the locking gate.

When the sensors of the selector fork and release fork detect shift state A (P-ON), solenoid N486 can be switched off. Spring force

causes the locking pin to extend; it lies against the end face of the gear wheel, removed from action.

Gear actuator VX65

It communicates with motor control unit J623 as a slave control unit via a sub-bus system (motor control unit CAN bus). As the

gear actuator is involved in the immobiliser system, it is secured with anti-theft bolts. A special bit insert VAS 6970 is required to

fit and tighten these bolts.

If the gear actuator or the transmission unit is renewed, the function “Work steps after component replacement” must be carried

out using the vehicle diagnostic tester via address word 0001 “Engine electronics, functions”.

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Shift drum positions and the resulting shift states

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The motor control unit determines the desired gear/the desired shift state and delivers this information to gear actuator VX65. In

doing so, it is influenced by the current Audi drive select mode, load requirement and speed (see shift programme).

Depending on the desired shift state, gear actuator VX65 turns the shift drum via the spur gear drive. The angle that the shift drum

turns results in shift state A, B, C or D for the dog clutch/the multi-plate clutch.

When switching from state A to state D, the shift drum control logic requires going through states B and C.

Shift state A

The multi-plate clutch and the dog clutch are engaged. In conjunction with the locking effect of the freewheel, the entire transmis-

sion unit is blocked. Shift state A is applied for the parking lock function (see shift matrix).

In the case of a defective selector mechanism, the parking lock function can be disengaged using the diagnostic tester and the

function 0001 Activation - release of parking lock. For this to be possible, the shift drum actuators must be intact, motor control

unit J623 must be able to actuate gear actuator VX65, and the vehicle electrics must have sufficient power. There is no provision

for mechanically releasing the parking lock function.

Shift state B

The multi-plate clutch is disengaged and the dog clutch is engaged. This shift state is applied in 1st gear, when recuperating in 1st

gear, for reversing or for transmission position N (see shift matrix). Transmission position N is used to deactivate the parking lock

function (P-OFF); it also makes it possible to push the vehicle and provides the car wash function.

Shift state C

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This shift state constitutes the preparation for shifting into 2nd gear. If the multi-plate clutch is already disengaged, the first step

is to disengage the dog clutch. This allows the sun gear of the planetary gear set to start rotating in the direction of the freewheel

(it will overtake the freewheel) as the clutch closes.

State C is also shifted through when shifting from 2nd gear back into 1st gear. When the multi-plate clutch disengages, the plane-

tary gear is no longer blocked. The planetary gears start to move and transmit power to the sun gear to provide the speed reduction

for 1st gear. For this to happen, the sun gear must be held in locking direction by the freewheel; it is stationary.

Transition from shift state C to B

Before the dog clutch engages, it must be ensured that 1st gear is able to transmit power. This likewise ensures that the sun gear,

and therefore the rotor of the dog clutch, is not moving and that it is already possible to engage the non-synchronised dog clutch

during driving.

The dog clutch is engaged in order to recuperate in 1st gear and to enable driving in reverse gear.

Shift state D

The multi-plate clutch engaged and the dog clutch is disengaged. This shift state is applied in 2nd gear (see shift matrix).

Shift program

Audi drive se-

lect mode

Drive torque distribution

Driving off for-

wards

During driving

2nd gear

Shifting to speed reduction for 1st gear

[4]

efficiency

comfort

dynamic

Front axle prioritised

For reverse gear and in the case of spe-

cial shifting behaviour

2nd gear

[4]

Economical four-wheel drive

prioritised

2nd gear

Yes, below approx. 50 km/h with high

load requirement and for reverse gear

2nd gear

Performance-oriented four-

wheel drive

1st gear

2nd gear from ap- Yes

prox. 70 -

110 km/h

The motor control unit selects the desired gear according to the Audi drive select mode, load requirement and vehicle speed.

The shift drum actuators apply the selected gear.

Audi drive select mode “efficiency”

The transmission unit remains exclusively in 2nd gear to provide maximum range. Only in transmission position R is the shift state

for 1st gear applied to provide reverse gear.

Reverse gear is then applied by reversing the direction of rotation of the electric motor.

Audi drive select mode "comfort"

In comfort mode, the vehicle drives prioritises 2nd gear for driving off, and remains in 2nd gear. The vehicle only switches to 1st

gear to provide maximum performance at speeds below approx. 50 km/h with a very high load requirement from the driver.

Audi drive select mode "dynamic"

In dynamic mode, the vehicle drives off in 1st gear. Depending on the load requirement, the vehicle shifts into 2nd gear starting

from speeds between approx. 70 km/h and 110 km/h. As a rule, the vehicle shifts back into 1st gear if the driving speed falls below

this range. The exact speed at which the downshift occurs depends on how the vehicle is being driven.

Special shifting behaviour

When the vehicle is driven in transmission position D, 2nd gear is normally used for driving off. If position R is selected and then

position D, 1st gear remains selected initially. Only after reaching a driving speed above approx. 20 km/h does the vehicle shift into

2nd gear.

[4] Driving off in 1st gear is also possible; see “special shifting behaviour”

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Transmission schematic

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The gearbox schematic shows the gearbox when the vehicle is stationary and in transmission position N.

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Shift matrix

Trans-

mission

posi-

Dog clutch

Multi-plate

clutch

Free-

wheel

Remarks

tion/

gear

Drive

R

Engaged

Disengaged

Reverse gear is applied by reversing the direction of rotation of the

electric motors. The planetary gear set of two-speed transmission

0ME acts as a speed reduction stage in the same way as for 1st

gear. The torque is transferred via the sun gear which is blocked by

the dog clutch.

(pre-loaded) (actuated)

N

P

Engaged

Disengaged

The transmission unit does not have a neutral position, i.e. there is

no shift position in which the power flow between the electric drive

motor and the wheels is interrupted. Transmission position N cor-

responds to the shift position for 1st gear and reverse gear.

(untensioned) (actuated)

Engaged

Blocked

The transmission unit does not have a physical parking lock. By

blocking the entire planetary gear set (annulus with planet carrier

and sun gear in both directions), the gearbox is blocked; this serves

as the parking lock function.

(pre-loaded

when rolling

forwards)

(not actuated)

(when

rolling

back-

wards)

D1

D2

Closed

Disengaged

Blocked

The planetary gear set serves as a speed reduction stage. The tor-

que is transferred via the sun gear which is blocked by the free-

wheel.

(untensioned) (actuated)

Open

Engaged

Freewheel The planetary gear set is blocked. Annulus, sun gear and planet

carrier rotate at the same speed.

(not actuated)

Disengaged

Recu- D1

pera-

tion

Closed

The planetary gear set serves as a speed reduction stage. The direc-

tion of power flow is reversed. The torque is transferred via the sun

gear which is blocked by the dog clutch.

(pre-loaded) (actuated)

D2

Open

Engaged

Freewheel The planetary gear set is blocked. Annulus, sun gear and planet

carrier rotate at the same speed.

(not actuated)

The direction of power flow is reversed without affecting the free-

wheel.

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Power flow

Single-speed, D1, transmission

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Key:

Torque curve/power flow

Blocked, stationary components

Parts which co-rotate without being involved in power flow

Engaged, blocked, engaged for power transmission

Components joined to housing

Clutch

Power flow arrow

Transmission po- Dog clutch

Multi-plate clutch Freewheel Remarks

Disengaged Blocked

(untensioned) (actuated)

sition/gear

Drive D1

Closed

The planetary gear set serves as a speed reduction stage.

The torque is transferred via the sun gear which is blocked

by the freewheel.

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Single-speed, D1, recuperation

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Key:

Torque curve/power flow

Blocked, stationary components

Parts which co-rotate without being involved in power flow

Engaged, blocked, engaged for power transmission

Components joined to housing

Clutch

Power flow arrow

Transmission

position/gear

Dog clutch Multi-plate clutch Free-

Remarks

wheel

Recuper- D1

ation

Closed

Disengaged

The planetary gear set serves as a speed reduction stage.

The direction of power flow is reversed. The torque is trans-

ferred via the sun gear which is blocked by the dog clutch.

(pre-loaded) (actuated)

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Reversing in 1st gear

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Key:

Torque curve/power flow

Blocked, stationary components

Parts which co-rotate without being involved in power flow

Engaged, blocked, engaged for power transmission

Components joined to housing

Clutch

Power flow arrow

Transmis-

sion posi-

tion/gear

Dog clutch Multi-plate

clutch

Free-

wheel

Remarks

Drive R

Engaged

Disengaged

Reverse gear is applied by reversing the direction of rotation of the

electric motors. The planetary gear set of two-speed transmission

0ME acts as a speed reduction stage in the same way as for 1st gear.

The torque is transferred via the sun gear which is blocked by the dog

clutch.

(pre-loaded) (actuated)

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2-speed, D2

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Key:

Torque curve/power flow

Blocked, stationary components

Parts which co-rotate without being involved in power flow

Engaged, blocked, engaged for power transmission

Components joined to housing

Clutch

Power flow arrow

Planetary gear set in blocking mode/blocked

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Transmission Dog

Multi-plate clutch Freewheel Remarks

position/

gear

clutch

Drive

D2

Open

Engaged

Freewheel The planetary gear set is blocked. Annulus, sun gear and planet

carrier rotate at the same speed.

(not actuated)

Engaged

Recuper- D2

ation

Freewheel The planetary gear set is blocked. Annulus, sun gear and planet

carrier rotate at the same speed. The direction of power flow is

reversed without affecting the freewheel.

(not actuated)

As the planetary gear set is blocked by the multi-plate clutch, the torque is transmitted directly from the planet carrier to the annu-

lus. The planetary gears and the sun gear do not affect the drive torque or the overrun torque during recuperation.

The reversed direction of power flow during recuperation does not affect the freewheel.

Transmission position P

Parking lock function when rolling forwards

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Transmission Dog clutch

position/

gear

Multi-plate

clutch

Freewheel

Remarks

P

Engaged

Blocked

The transmission unit does not have a physical parking lock.

By blocking the entire planetary gear set (annulus with

planet carrier and sun gear in both directions), the gearbox

is blocked; this serves as the parking lock function.

(pre-loaded when (not actuated)

rolling forwards)

(when rolling

backwards)

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Parking lock function when rolling backwards

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Key:

Torque curve/power flow

Blocked, stationary components

Parts which co-rotate without being involved in power flow

Engaged, blocked, engaged for power transmission

Components joined to housing

Clutch

Power flow arrow

Planetary gear set in blocking mode/blocked

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Function diagram, 2-speed transmission 0ME

65

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Key:

E313

Selector lever

G38

Gearbox speed sender

G79

Accelerator position sender

Gearbox oil temperature sender

Brake pedal position sender

Accelerator position sender 2

Clutch position sender

G93

G100

G185

G476

G836

G1016

GX2

Brake pedal position sender 2

Clutch jaw position sensor

Accelerator pedal module

J533

J623

J1235

Data bus diagnostic interface

Engine control unit

Electric drive control unit for rear axle

N486

NX6

Parking lock solenoid

Brake servo

V552

VX65

Gearbox auxiliary hydraulic pump

Gear actuator

Earth wire

Positive wire

LIN bus

Sensor wire

FlexRay

FlexRay Low

Sub-bus system (motor control unit CAN bus) High

Sub-bus system (motor control unit CAN bus) Low

CAN bus High (Infotainment)

CAN bus Low (Infotainment)

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Sensors

Clutch position sender G476

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Clutch position sender G476 helps register the shift state of the multi-plate clutch. It is bolted onto the gearbox housing from the

outside. If repairs are required, only the bolts listed in the electronic parts catalogue (ETKA) for this purpose may be used.

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The shift state of the multi-plate clutch is registered indirectly based on the position of the release fork. The release fork is fitted

with a bracket on which a small magnet is secured. This is used to register the position of the release fork. When the position of the

release fork changes, the magnet moves along below clutch position sender G476.

Clutch position sender G467 is supplied with current (approx. 5 V) by motor control unit J623. It registers the movement of the

[5]

magnet and uses it to generate a PWM signal . Using this signal, the motor control unit determines the shift state of the multi-

plate clutch.

The information regarding the shift state of the multi-plate clutch is also used to determine the state of the parking lock function

(P-ON/P-OFF).

If clutch position sender G476 fails, no gear changes take place during driving.

If clutch position sender G476 is renewed, the function “Work steps after component replacement” must be carried out using the

vehicle diagnostic tester via address word 0001 “Engine electronics, functions”.

[5] PWM = pulse-width modulation

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Sensor concept

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Clutch position sender G476 works like a differential transformer. The centre part of the magnetically soft core is wrapped with a

primary coil. The core has a secondary coil at each end which is wound in the opposite direction. The primary coil is supplied with

alternating voltage, and thereby also induces alternating voltage in the secondary coil.

When the magnet is in the centre of the sensor, the induced voltages in the secondary coils (wound in the opposite direction) can-

cel each other out. If the magnet is pushed out of the centre, a difference in voltage arises at the secondary coils. The sensor elec-

tronics use this to generate a PWM signal that corresponds to the position of the magnet.

Reference

For further information on this sensor concept, please refer to SSP 241 "The Audi allroad quattro with additional shift

stage", starting on page 56.

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Clutch jaw position sensor G1016

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Clutch jaw position sensor G1016 registers the shift position of the dog clutch. It is bolted onto the gearbox housing from the out-

side. If repairs are required, only the bolts listed in the electronic parts catalogue (ETKA) for this purpose may be used.

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The position of the stator of the dog clutch is used to determine the shift state of the dog clutch. A small magnet is fitted on the

stator for this purpose. When the position of the stator changes, the magnet moves along below clutch jaw position sensor G1016.

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Sensor G1016 is supplied with current (approx. 5 V) by motor control unit J623. It registers the movement of the magnet and uses

[5]

it to generate a PWM signal . Using this signal, the motor control unit determines the shift state of the dog clutch.

The information regarding the shift state of the dog clutch is also used to determine the state of the parking lock function (P-ON/P-

OFF).

If clutch jaw position sensor G1016 fails, no gear changes take place during driving. If clutch jaw position sensor G1016 is re-

newed, the function “Work steps after component replacement” must be carried out using the vehicle diagnostic tester via address

word 0001 “Engine electronics, functions”.

Sensor concept

Clutch jaw position sensor G1016 works in the same way as clutch position sender G476.

Gearbox oil temperature sender G93

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Gearbox oil temperature sender G93 measures the gear oil temperature in the oil pan and sends this information to motor control

unit J623. The gear oil temperature measured is used to deduce the temperature of the multi-plate clutch.

To ensure that the multi-plate clutch is cooled sufficiently, the delivery volume from the electric gear oil pump is varied according-

ly.

The table lists the measures that are carried out and the messages that are shown in the instrument cluster to protect the compo-

nents and the gear oil at oil temperatures above approx. 110 °C.

If sender G93 fails due to a defect, the delivery rate of gearbox auxiliary hydraulic pump V552 is increased accordingly, and the

torque of the electric drive motor is reduced. In addition, the launch control function is not available.

The instrument cluster shows the yellow warning lamp and the message:

Gearbox malfunction: you can continue driving

[5] PWM = pulse-width modulation

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Oil temperature Measure

Displays/messages

Gearbox overheating: please adapt driving

> 110 °C

> 120 °C

> 130 °C

Torque of electric drive motor reduced. Launch control not

available.

style.

Additionally, forced shift into 2nd gear with downshifting pro-

hibited.

Gearbox overheating: please adapt driving

style.

Maximum speed reduced additionally.

Gearbox overheating: please stop vehicle

Gearbox speed sender G38

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Gearbox speed sender G38 helps the power electronics J1235 determine the following information:

›

Gearbox output speed

Direction of travel

Slip in multi-plate clutch

Target speed for gear change

Speed sender G38 is composed of three Hall elements arranged in series, a permanent magnet and sensor electronics to generate a

square wave signal. The large spur gear of the final drive acts as the sender wheel.

The sender is supplied with a 5-Volt current by the power electronics J1235. The sensor electronics use the signals from the individ-

ual Hall elements to determine the speed and direction of rotation of the gear wheel.

The direction of rotation of the gear wheel is indicated by the duration of the square-wave signal.

›

The signal duration when driving forwards is 120 μs

The signal duration when reversing is 60 μs

The speed of the gear wheel (proportional to the vehicle speed) is indicated on the basis of the frequency (f) with which the square-

wave signal occurs. The frequency corresponds to the inverse value of the cycle duration (T).

72

At frequencies of 1000 Hz and above (which corresponds to a vehicle speed of approx. 75 km/h), the cycle duration is reduced to

30 μs as a general rule.

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Measures if there is slip in the multi-plate clutch

Motor control unit J623 receives information on the speed of the electric drive motor and the gearbox output speed of the power

electronics J1235. It uses these two speeds to calculate the slip in the multi-plate clutch.

The table lists the measures that are carried out and the messages that are shown in the instrument cluster if there is slip in the

multi-plate clutch that should not be present (depending on the amount of slip):

As the parking lock function is carried out in part by the multi-plate clutch, this function may not be available if there is too much

slip in the clutch. If there is slip in the clutch, the transmission unit can no longer be used reliably to prevent the vehicle from roll-

ing away.

When the vehicle is stationary, the warning message Vehicle may roll away! P cannot be selected. Please apply parking appears in

the instrument cluster, and the yellow warning lamp lights up.

The vehicle can then be prevented from rolling away only by applying the parking brake.

Clutch slip Measure

Displays/messages

Gearbox malfunction: you can continue driving

Sporadic

Torque of electric drive motor reduced.

Constant Torque of electric drive motor reduced. Additionally: Forced

shift back into 1st gear and therefore reduced maximum

speed; upshifting prohibited.

Gearbox malfunction: you can continue driving

No parking lock function.

Vehicle may roll away! P cannot be selected.

Please apply parking brake

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Oil system

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Gearbox auxiliary hydraulic pump V552

Gearbox auxiliary hydraulic pump V552 supplies the transmission with lubricating/cooling oil as required. The oil pump draws gear

oil out of the oil pan via the suction filter and conveys the oil to all areas requiring lubrication via oil pressure lines and oil passages

in the transmission housing.

The pump consists of a brushless DC motor that drives an annular gear pump, as well as integrated power electronics. Motor con-

trol unit J623 evaluates the amount of lubrication and cooling required for the current operating state, and uses this to determine

the required pump speed.

The information exchanged between motor control unit J623 and the oil pump is transmitted via a separate LIN bus.

After the drive system is activated, the oil pump is actuated briefly to lubricate all the components. If the vehicle remains station-

ary, the oil pump is actuated briefly approx. every 20 seconds, irrespective of the transmission position currently selected.

As soon as the vehicle is driven, motor control unit J623 actuates the oil pump as necessary. The pump speed is regulated according

to the following parameters:

›

The calculated input torque of the transmission,

The gearbox output speed,

The selected gear,

The oil pan temperature,

The lateral/longitudinal acceleration of the vehicle

Oil pump V552 sends a speed signal back to motor control unit J623 in a closed feedback loop. This allows the motor control unit

to re-adjust the pump speed if necessary and ensure that the required amount of lubrication/cooling for the transmission is provi-

ded.

74

If the pump speed drops when it should not, or if the pump fails, the following measure are taken:

Cause

Measure

Displays/messages

Slight drop in pump speed, Speed is re-adjusted

e.g. oil filter dirty

No display/messages

Significant drop in pump

speed

Torque of electric drive motor reduced. Launch control not

available.

Gearbox: fault. Safely stop ve-

hicle

Additionally, forced shift into 2nd gear with downshifting pro-

hibited and reduced maximum speed.

No pump speed signal

See “Significant drop in pump speed”

Gearbox: fault. Safely stop ve-

hicle

Oil cooler

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The gear oil cooler is an oil/coolant heat exchanger. It is integrated in the coolant circuit for the electric powertrain. There is no

separate switching valve to decouple the oil cooler from the coolant circuit for the electric powertrain. If the electric drive motor

and the power electronics for the rear axle are being cooled, the gear oil for the two-speed rear transmission unit is cooled auto-

matically.

75

Oil filler and inspection plug and oil drain plugs

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Two-speed transmission unit 0ME has two oil drain plugs to allow the oil to be drained completely. The hole for the oil filler plug is

used to top up the oil and check the oil level. Please refer to the current workshop information for specifications on the oil capacity

and oil type.

Active rear axle differential lock

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The Audi e-tron GT is available with an active rear axle differential lock as optional equipment. This differential lock is fitted as

standard equipment on the Audi RS e-tron GT. The active differential lock can lock the speed equalisation function in the differen-

tial as desired using a multi-plate clutch.

Axle differential lock control unit J647 calculates the desired lock value and actuates axle differential lock motor V304 accordingly.

The two axle differential lock Hall senders G460 and G461 and temperature sender G1175 are contained inside axle differential

lock motor V304. The Hall senders allow axle differential lock control unit J647 to infer the position of the rotatable ball ramp ring,

and the temperature sender provides information on the thermal load of the motor.

76

Depending on the desired lock value, axle differential lock motor V304 turns the adjusting ring for the clutch engagement mecha-

nism via reduction gearing. The main components of the clutch engagement mechanism are a ball ramp ring, which can move

along the shaft and is mounted so that it does not rotate, the ball bearings and a ball ramp ring that does rotate (referred to as the

adjuster ring). The rotational movement of the adjusting ring creates axial movement which pushes the clutch plates together.

The active differential lock works together with the selective wheel torque control of ABS control unit J104 to prevent the wheels

from spinning.

The two systems therefore improve:

›

The torque distribution

The traction

The lateral acceleration potential

The driving stability during changes in load when cornering

The handling when changing lanes

The stability in overrun phases

This makes faster cornering speeds possible. The effect of the differential lock and any application of the brakes by the system are

particularly noticeable when driving on surfaces that offer little traction, such as wet or snowy roads.

In contrast to a conventional differential lock (see SSP 613 "Audi R8 Power Transmission", page 28), the active differential lock can

be opened completely. This means that the rear brakes can be activated without interference if ABS control unit J104 intervenes.

Note

Axle differential lock control unit is fitted at the rear right inside the luggage compartment. If axle differential lock

control unit J647 is renewed, the new control unit must be activated using the vehicle diagnostic tester. If axle differ-

ential lock motor V304 is renewed, it must be adapted using the vehicle diagnostic tester to account for component

tolerances.

77

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Function diagram - active rear axle differential lock

684_361

Key:

G460

G461

G1175

Axle differential lock Hall sender 1

Axle differential lock Hall sender 2

Temperature sender for axle differential lock motor

J233

J533

J623

Adjustable rear spoiler control unit

Data bus diagnostic interface

Motor control unit

79

Power transmission -> Two-speed transmission 0ME for Your Audi RS E Tron Gt 4 Door First Generation (2021-2026)

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