and the Lamborghini Huracán.

19

Component overview

Electrical connection/circuit board
for parking lock module

Parking lock mechanism and parking lock
emergency release mechanism

Electro-hydraulic parking lock
›› Parking lock module

Final drive with differential lock
›› The locking characteristics have been adapted to the
quattro drive concepts
›› For more information on the differential lock refer
to eSSP 950123, Audi R8 Power Transmission

Dual clutch

20

Automatic Transmission Control
Module 2 J1006

Parking lock gear

Gear set and gear actuator
›› Hydraulically operated selector plates

Electrical connection of mechatronic
unit

Electro-hydraulic gearbox control module
›› Dual-Clutch Transmission Mechatronic
J743
›› Gearbox Control Unit 1 J743

Auxiliary hydraulic module
›› ATF pump
›› Electro-hydraulic control unit

Electrical connection for
auxiliary hydraulic module

Electrical connection for
auxiliary hydraulic module

643_038
21

Gear set/gear train configuration
A dual clutch transmission consists of two gear train subsets
and two associated clutches - K1 and K2. Gear train subset 1
carries the uneven gears 1, 3, 5, 7 and gear train subset 2 the
even gears 2, 4, 6 and reverse.
In operation, only one gear train subset is transmitting power
at a time, while on the other gear train subset the next gear
required is pre-engaged. If, for example, the vehicle is accelerating in 3rd gear, the next gear required is 4th gear on gear
train subset 2.

Rear axle final drive

Gear changes are performed by switching power transmission
from one clutch to the other. In the above example –
changing from 3rd to 4th gear – clutch K2 is engaged while
clutch K1 is simultaneously disengaged.
That process is referred to clutch overlap or overlap gear shifting. The entire sequence takes place in only a few hundredths
of a second. The dual clutch gearbox enables quicker gear
shifts which reduce power flow interruption.

Differential gear
with differential lock

Spur gear for driving ATF pump

K2
Dual-mass flywheel for isolating
rotational vibration

Crankshaft

Front final drive input shaft
›› The final drive input shaft is also referred to
as the PTO shaft.

Output shaft transmission ratios
›› Basic transmission ratio on V10:
28 : 23
›› Dynamic transmission ratio on V10 Plus: 28 : 21

22

K1

The rear final drive uses bevel gears without hypoid offset.
That means that the sliding forces between the meshing
teeth are smaller than with bevel gears with hypoid offset.
This design enables the use of a common oil system using
low-viscosity ATF for all functional transmission subassemblies.
The differential has a differential lock design carried over
from the R tronic. More detailed information on the differential lock can be found in eSSP 950123, Audi R8 Power
Transmission. The locking characteristics have been
adapted to suit the all-wheel drive concept of the 2017 R8.

Pinion shaft

R

1
4

5

Output shaft 1

Input shaft 1

Output shaft 2

7

6

3

2

Gearbox unit 1
Input shaft 2

Gearbox unit 2
643_039

23

Dual clutch
The dual clutch is the central functional component of the
dual clutch transmission. It transmits the torque to the
relevant gear train subset.

Design features
The dual clutch consists of two wet-type multi-plate clutches,
K1 and K2. The two clutches are mounted in line with each
other and have the same dimensions and the same number of
plates.

Power transmission path in the dual clutch
The engine torque is transmitted from the dual-mass flywheel via the dog clutch to the coupling housing and from
there to the clutch housing cover. The clutch cover positively
interlocks with the clutch hub. The clutch hub, in turn, is
connected to the inner plate carriers of the two clutches.
Clutch K1 transmits the torque to its outer plate carrier,
which in turn positively interlocks with input shaft 1. Clutch
K2 transmits the torque to input shaft 2.

Reluctor for engine speed sensor

Clutch housing

Piston K2

K2

K1

MEngine

Piston K1
Clutch housing cover

Clutch hub –
inner plate carrier
Clutch carrier

Driving device

24

Input shaft 1

Input shaft 2

643_040

Dual mass flywheel

Driving device

Clutch cover

Clutch housing cover

K2
K1

Ring gear –
for starter

Dowel sleeve

ATF pump drive
Clutch hub –
inner plate carrier

Clutch carrier

Sections through fixed components – gearbox housing
Power transmission path from dog clutch to clutch
643_041
25

Dual clutch oil system
The oil entire oil system for the dual clutch is supplied via the
clutch carrier by means of a rotational feed system.
The dual clutch is mounted on the clutch carrier by two
needle roller bearings. See Figure 643_041 on page 25.
The clutches are supplied with the control pressure (clutch
pressure), cooling oil and centrifugal oil for dynamic pressure
equalization via four oil channels. Five Torlon rings form the
rotary seals for the four oil channels.
In order to counterbalance the effect of dynamic pressure
build-up with increasing rotational speed, each of the
clutches has a pressure equalization chamber (centrifugal oil
chamber).

Clutch cooling
Each of the two clutches has a separate and demand-based
cooling and lubrication oil supply (clutch cooling system). For
that purpose, the centrifugal oil temperature of each clutch is
detected by a separate temperature sensor (G658/G659).

The following functions are associated with the dual clutch:
››
››
››
››
››
››
››
››
››
››

Clutch control.
Dynamic pressure equalization.
Start-up.
Power flow reversal.
Clutch cooling.
Clutch control at standstill (creep control).
Overload protection.
Safety shut-off.
Microslip control.
Clutch adaptation.

Basic information about those functions is provided in eSSP
951403, The O2E Direct Shift Gearbox, Design and Function.

Clutch pressure, clutch K1

Clutch pressure, clutch K2

Dual-Clutch Transmission
Mechatronic J743

The supply of oil for cooling and lubricating the clutches is
provided via the centrifugal oil chambers.
A special feature of the clutch cooling system on the 0BZ
transmission is that the cooling oil supply for clutch K1 provided by the Mechatronic module while the cooling oil supply
for clutch K2 is provided by the auxiliary hydraulic module.
The clutch cooling system for clutch K2 is controlled by
Clutch Cooling Valve 2 N488. Which in turn is controlled by
Automatic Transmission Control Module 2 J1006.

Clutch cooling system for clutch K1
Gearbox Control Unit 1 J743 registers the centrifugal oil
temperature of clutch K1 from Clutch Temperature Sensor 1
G658 and calculates the control current for Clutch Cooling
Valve 1 N447.

Clutch cooling system for clutch K2
Automatic Transmission Control Module 2 J1006 registers the
centrifugal oil temperature of clutch K2 from Clutch Temperature Sensor 2 G659 and sends the information to
Gearbox Control Unit 1 as a CAN message. It calculates the
required control current for Clutch Cooling Valve 2 N448 and
send that information to Automatic Transmission Control
Module 2 J1006. J1006 then applies the specified current to
N448.

Clutch cooling oil/centrifugal oil,
clutch K1

26

Clutch Cooling Valve 2
for clutch K2

Clutch monitoring
The temperature of the two clutches is continuously monitored by J743 and J1006.

The clutch pressure of the two clutches is continuously
monitored by Gearbox Control Unit 1 J743. If the pressure
deviates from the specified clutch pressure, the clutch
concerned is de-pressurized by means of a safety cut-out.
Refer to page 60.

Two temperature sensors, G658 and G659, are used to calculate the clutch temperature and controlling clutch cooling.
If a centrifugal oil temperature of around approximately
338 °F (170 °C) is exceeded, the instrument cluster displays
the warning "Gearbox too hot. Please adjust driving style."
and a corresponding DTC is registered in the control module.

Pressure equalization chamber – centrifugal oil chamber, clutch K1

Clutch piston, clutch K1
Pressure equalization
chamber – centrifugal oil
chamber, clutch K2

Pressure chamber K1

Clutch piston, clutch K2

Pressure chamber K1

KD2
KK1

KK2
KD1
Torlon ring

K2
K1

643_042

Key:

Auxiliary hydraulic module

Clutch cooling oil/centrifugal oil, clutch K2

KD1

Clutch pressure oil channel, clutch K1

KK1

Cooling oil/centrifugal oil channel, clutch K1

KD2

Clutch pressure oil channel, clutch K2

KK2

Cooling oil/centrifugal oil channel, clutch K2

27

Gear train and gear set
Special features
The gear set of the 0BZ transmission has the following
special features:
›› Reverse gear is implemented without a separate reverse
drive gear or reverse shaft.
›› The parking lock gear is combined with the sliding collar of
gear set R/4 in a single unit.
›› There is a separate output shaft for driving the front
wheels.

Output shaft 1

Sliding collar R/4 with parking lock gear

Input shaft 2

Input shaft 1

Output shaft 2

Pinion shaft

Different output shaft transmission ratios
›› Basic transmission ratio on V10:
28 : 23
›› Dynamic transmission ratio on V10 Plus: 28 : 21

643_043

Figure 643_045 opposite shows how the two output shafts 1
and 2, the pinion shaft and the PTO shaft for the front final
drive are permanently engaged.

28

Front final drive input shaft (PTO)

Disengage

Reverse gear

The parking lock gear is located on the sliding collar of gear
set R/4. The sliding collar, the synchromesh hub and output
shaft 1 are locked together rotationally. When the parking
lock is engaged, output shaft 1 is locked.

The reversal of rotation direction for reverse gear is achieved
by means of the synchronizer gear for 2nd gear. The synchronizer gears for 2nd and reverse gears are permanently
engaged. In reverse gear, the torque is transmitted from
input shaft 2 via the idling synchronizer gear for 2nd gear to
the synchronizer gear for reverse gear. The direction of
rotation of output shaft 1 is opposite to what it is in the
forward gears.

Reverse gear

Output shaft 1
Synchro hub
Sliding collar R/4
with parking lock
gear
Input shaft 2

Output shaft 2

2nd gear pinion

643_044

Interconnection of the shafts

Output shaft 1

Output shaft 2

Pinion shaft
643_045
29

Gear shifting and gear-shift actuators
Gear changing is performed by means of four hydraulically
operated selector forks referred to as gear-shift actuators.

Selector fork 1, gear-shift
actuator A
5th/1st gear

Each gear-shift actuator consists of a selector fork with a
selector plate at each end of which is a single-action hydraulic
cylinder. On the selector plate there is also a bracket holding
sensor magnets and a catch.
Pressure is applied to the hydraulic cylinders so that they
move the selector forks to the left or right (gear engaged),
depending on the gear to be selected, or to the center position (neutral position). Once the gear/neutral position is
engaged, the hydraulic cylinders are de-pressurized. The
gears are kept engaged by the undercut of the dog teeth and
the catches on the selector plates. In neutral position, the
selector plates are held in the center position by the catches.
The sliding collars also have a catch for the neutral position.
When the vehicle is stationary, 1st gear is always engaged on
gear train subset 1. On gear train subset 2, 2nd or reverse
gear may be engaged depending on the preceding driving
scenario. If the vehicle is braked to a standstill after travelling
forwards, 2nd gear remains engaged. Reverse gear is not
engaged until transmission setting R is selected or if the
engine is switched on again after being switched off and
transmission setting D or R is selected. If, for example, the
engine is switched off immediately after backing up, reverse
gear remains engaged.

Selector plate catch
Selector fork 1, gear-shift
actuator A,
gears 5/1

Selector fork 4, gear-shift actuator D,
gears R/4

Gearbox unit 1
Gearbox unit 2
643_046

30

Gear shift monitoring
For the transmission to function perfectly, the exact positions
of the selector forks must be known by transmission control
module.
Four travel sensors, aided by sensor magnets attached to the
selector rods, define the positions of the relevant gear shift
actuators/selector forks. Refer to page 68.

643_047

The measurements taken – actual positions of gear-shift
actuator A (B/C/D) – show the gear-shift travel in millimetres. Refer to page 68.
Travel of gear-shift
actuator

Sensor magnet for Gear Position Distance Sensor 4
G4901) for gear-shift actuator D for gears R/4

3rd/4th/5th/6th gear
engaged

Sensor magnet for Gear Position Distance Sensor 1
G4871) for gear-shift actuator A for gears 5/1

Neutral position

1st/2nd/7th/Reverse
gear engaged

643_102

In the event of malfunctions or invalid shift positions, the
gear train subset concerned is hydraulically disabled by
means of the safety cut-out. Refer to page 60.
Selector fork 3/gear-shift actuator C, gears 3/7

Sensor magnet for Gear Position Distance Sensor 3
G4891) for gear-shift actuator C for gears 3/7

Due to manufacturing tolerances, the limit positions and
synchronization points of each gear have to be learned by
Dual-Clutch Transmission Mechatronic J743. This can be done
via the VAS Scan Tool.

Sensor magnet for Gear Position Distance Sensor 2
G4881) for gear-shift actuator B for gears 2/6
Selector fork 2/gear-shift actuator B, gears 2/6

1)

See also page 68.

31

Power transmission path in gearboxes
1st gear

Pinion shaft

Gearbox unit 1
Gearbox unit 2
Input shaft 1
Input shaft 2

R

1
4

Output shaft 1

5

K2 K1

PTO shaft for front
final drive

2

7

6