Self Study Programme 620
For internal use only
Audi
ACC Systems
Audi
Service Training
Adaptive Cruise Control (ACC) systems
Recent years have been characterised by rapid development in the
field of driver assist systems. This has been made possible by
technological progress, specifically in the development and production of electronic components.
The complexity of available functions is also growing due to the
shared use of subfunctions by various vehicle systems, as well as
by increasing information exchange between vehicle systems. It is
predicted that piloted driving will become a technical reality even
during this decade. Adaptive Cruise Control (ACC) is one of the
basic systems which laid the foundation for this development
when it was first introduced on the Audi A8 in 2003. In the course
of this evolutionary process, the range of functions of the ACC
system has steadily grown and this system is today used in many
current Audi models.
A self study program (SSP 289) was previously published when the
ACC system was introduced on the Audi A8 in 2003. The range of
functions of ACC has since been significantly extended by, in
particular, including measured data provided by other sensors.
Further system improvements have extended the system's limits
and greatly increased system availability.
This self study programme serves as an update to the existing SSP
289. It also provides an overview of the ACC systems used in
current Audi models. Another key topic is the additional functions
complementing the ACC basic function. In the area of service,
special attention is given to the procedure for setting the current
ACC systems with two radar sensors.
Understanding the functional relationships between systems is a
major challenge for service personnel. This knowledge is indispensable when it comes to explaining to customers how systems work
and performing function tests as well as identifying, diagnosing
and, ultimately, correcting faults.
620_001
2
Contents
ACC basic function
Overview ______________________________________________________________________________________________________________________________________________________ 4
Technische implementation - radar technology __________________________________________________________________________________________________________ 6
The distance measurement process _______________________________________________________________________________________________________________________ 6
Determining the speed of the vehicle ahead ______________________________________________________________________________________________________________ 8
Example showing how the speed and distance of the vehicle ahead are determined _________________________________________________________________ 9
Determining the position of the vehicle ahead __________________________________________________________________________________________________________ 10
Determining the vehicle relevant to ACC _________________________________________________________________________________________________________________ 11
Adaptive Cruise Control (ACC) - system limitations _____________________________________________________________________________________________________ 12
Description of ACC system
ACC options __________________________________________________________________________________________________________________________________________________ 13
System parameters _________________________________________________________________________________________________________________________________________ 14
System components ________________________________________________________________________________________________________________________________________ 16
Networking - data transfer _________________________________________________________________________________________________________________________________ 20
Operation and driver information
ACC on/off _ __________________________________________________________________________________________________________________________________________________ 22
Setting the target speed ___________________________________________________________________________________________________________________________________ 22
Setting the target distance_________________________________________________________________________________________________________________________________ 23
Setting the drive program __________________________________________________________________________________________________________________________________ 23
Setting the gong volume ___________________________________________________________________________________________________________________________________ 24
System status indication ___________________________________________________________________________________________________________________________________ 24
How the driver is prompted to take over _ ________________________________________________________________________________________________________________ 24
Basic operation ______________________________________________________________________________________________________________________________________________ 24
ACC auxiliary functions
Overview _____________________________________________________________________________________________________________________________________________________ 25
Audi braking guard __________________________________________________________________________________________________________________________________________ 26
Evolution _____________________________________________________________________________________________________________________________________________________ 31
Audi Stop and go ____________________________________________________________________________________________________________________________________________ 32
Lane change assistance _____________________________________________________________________________________________________________________________________ 37
Service operations
Sensor vision _________________________________________________________________________________________________________________________________________________ 39
Replacement and removal/installation of the ACC sender with ACC control unit ___________________________________________________________________ 39
Calibrating the ACC sender _________________________________________________________________________________________________________________________________ 40
• The Self Study Programme teaches a basic knowledge of the design and mode of operation of new models,
new automotive components or new technologies.
It is not a Repair Manual! Figures are given for explanatory purposes only and refer to the data valid at the
time of preparation of the SSP.
This content is not updated.
For further information on maintenance and repair work, always refer to the current technical literature.
!
Information
Reference
3
ACC basic function
Overview
Adaptive Cruise Control is a systematic further development of the
cruise control system first introduced on the Audi A8 in 2003. If
the road ahead is clear, ACC acts in much the same way as a cruise
control system by adjusting the speed of the vehicle to the target
speed set by the driver. If it is not possible to travel at the desired
speed due to a slower-moving vehicle ahead, ACC maintains the
vehicle-to-vehicle distance set by the driver.
The vehicle is, if necessary, decelerated by reducing engine power,
by shifting down into a lower gear (on models with automatic
transmission) and/or by applying corrective braking. In certain
traffic situations, active braking of the vehicle by the driver is still
required and indicated by
audible and visual warnings.
No vehicle in front: the vehicle travels at the desired speed
Target distance
Vehicle ahead travelling slower than the desired speed: the desired vehicle-to-vehicle distance is maintained
4
620_002
To maintain a constant speed-dependent distance to a vehicle
ahead driving in the relevant lane, the ACC control software
requires the following information:
Distance to vehicle ahead
620_003
Speed of vehicle ahead
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Position of vehicle ahead
620_005
If there are multiple vehicles within the range of vision of the
radar, the system utilises the above information to select the
appropriate reference vehicle.
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5
Technische implementation - radar technology
Radar technology is used to to implement the ACC basic function.
Radar waves have advantages over optical systems due to their
short wavelength. Radar waves are absorbed and deflected to a
much lesser degree, especially in conditions of impaired visibility
(fog, driving snow). As a result, the system provides higher availability than optical systems.
Radio detecting and ranging (Radar) is an electronic process for
determining the position of objects.
The transmitted radar waves are reflected from suitable surfaces
and objects.
The time span between transmitting the signal and receiving the
reflected signal is dependent on the distance from the object.
The received waves reflected are correlated with the waves transmitted and evaluated.
The distance measurement process
A
Transmitter
Receiver
50 m
B
Transmitter
Receiver
100 m
620_008
This example shows the dependence of signal travel time on the
distance between the transmitter/receiver and object (see
diagram):
The vehicle-to-vehicle distance in case B is twice that in case A:
6
In case B the time which elapses until the reflected signal reaches
the receiver is twice that in case A.
Direct travel time measurement is a highly complex process. For
this reason, travel time is measured indirectly in the form of an
FMCW (Frequency Modulated Continuous Wave) process. Continuously emitted ultra-high frequency oscillations with a time-variable
frequency are used as a transmission signal.
A carrier signal in the frequency band between 76 and 77 Gigahertz acts as a "vehicle". This process eliminates the need for
complex direct travel time measurement. Instead, the more easily
determinable frequency differences between the signal transmitted and the signal received (=reflected) are evaluated.
Frequency
A
A
Time
± 200 MHz
B
B
The diagram shows the ± 200 Megahertz change in the frequency of the carrier signal due to
frequency modulation.
Frequency-modulated
(FM) signal
A
B
A
B
Time
While the amplitude (signal strength ) of the frequency-modulated signal stays almost
constant, the frequency (number of oscillations per unit of time) changes.
At the points in time marked A , the signal frequency in both diagrams has reached the
maximum value (greatest number of oscillations per unit of time). At the points in time
marked B, the signal frequency is at its lowest (least number of oscillations per unit of
time).
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7
Determining the speed of the vehicle ahead
A physical phenomenon called the "Doppler shift" is utilised to
determine the speed of the vehicle ahead. It makes a difference
whether the object reflecting the transmitted waves is stationary
or moving relative to the transmitter.
If the distance between the transmitter and object decreases, the
frequency of the waves reflected will increase. If the distance
increases, the frequency will decrease. The frequency shift is
evaluated by the electronics and indicates the speed of the vehicle
ahead.
Here is an example showing the effect of the
Doppler shift:
As the fire engine approaches, the observer hears a horn signal
which has a more or less constant high pitch (high frequency).
As the vehicle moves further away, the observer hears a lower
pitched tone (transition to lower frequency).
Pitch
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8
Example showing how the speed and distance of the vehicle ahead are determined
The vehicle ahead is driving faster and the vehicle-to-vehicle
distance is increasing. The frequency of the signal received
(reflected) decreases (D fD) due to the Doppler shift and is timeshifted on the basis of time elapsed between signals transmitted
and received.
This results in various differences in frequency between the rising
(D f1) signal edge and the falling signal edge (D f2). This differential is evaluated by the control unit.
Frequency
D fD
f1
Relative velocity
D f1
f2
f4
D f2
f3
620_011
Signal transmitted
Signal received/reflected
9
Determining the position of the vehicle ahead
The radar signal propagates in a conical fashion. Signal strength
(amplitude) decreases with increasing distance from the transmitter in the vehicle's longitudinal axis (x) and transverse axis (y).
y
x
Signal strength
x, y
620_012
To determine the position, the angle at which the vehicle ahead is
moving relative to one's self must be known. Transceiver units
equipped with four transmittes/receivers are used in current Audi
models to generate this information.
The position of the vehicle ahead can be determined exactly by
utilising the dependence of signal strength on the distance from
the transmitter in combination with the four radar beams. The
radar beams overlap one another on the periphery.
In the diagram, the vehicle ahead is detected simultaneously by
radar beams 2 and 3. If the vehicle in this example is to a greater
extent located within the range of signal 2, the signal strengths
(amplitudes) of signal 2 received (reflected) will be greater than
those of signal 3 received. The relationship between the strengths
(amplitudes) of the signals received from each of the radar beams
indicates the angle.
1
2
3
4
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10
Determining the vehicle relevant to ACC
In actual traffic situations (e.g. on motorways and multi-lane roads
or when cornering), it will often be the case that multiple vehicles
are simultaneously within the detection range of the radar. In such
situations, it is necessary to determine which vehicle is driving in
the same lane and to identify the vehicle to which the selected
distance is to be maintained. A prerequisite for this is that the
course of the road ahead can be determined by the ACC control
unit.
This is a relatively complex process based on measurement data
received from multiple sensors. The signals received from the
steering angle sender, the yaw rate sender and the wheel speed
sensor are utilised.
Depending on the vehicle's specification, additional lane markings
will also be identified by the camera. Crash barriers and lane
marker posts detected by the radar and the direction of travel of
other road users may also be used to determine the course of the
road ahead. If the vehicle is equipped with Navigation +, this
system's predictive route data is also used to determine the course
of the road ahead (this applies to the A6, S6, RS6, A7, S7, RS7 and
A8 models).
620_014
The ACC control unit determines this "fictitious" lane from the
actual curve radius R of the ACC-equipped vehicle and a predetermined average lane width B.
The nearest object (vehicle) to this lane is detected by the wheel
sensor and identified as the relevant vehicle. If the conditions for
ACC deployment are met, then the desired distance to this specific
vehicle will be maintained.
11
On winding roads or when entering or exiting curves, it may be the
case that a vehicle is briefly "lost" or that a vehicle travelling in the
adjacent lane is identified as the relevant vehicle.
As a consequence of this, the vehicle may be briefly accelerated or
braked by the ACC system. However, this is a relatively rare occurrence and is due to fact that the course of the road ahead cannot
be clearly identified.
Example
The ACC-equipped blue vehicle is following the red vehicle travelling in the same lane. On entering a corner, the blue vehicle is now
heading directly towards the oncoming green vehicle in the adjacent lane and may, in some situations, identify this as the reference vehicle. If so, this can lead to corrective adjustments which
will seem illogical to the driver.
620_015
!
Information
This control behaviour is system-related and not the result of a system fault!
Adaptive Cruise Control (ACC) - system limitations
• ACC is a driver assist system and not a safety system. It is not
designed for fully autonomous driving! ACC reduces the driver's
workload, but it does not relieve the driver of his responsibility!
• The effectiveness of the radar technology and the other relevant
sensors (video camera, ultrasound sensors) is limited by adverse
ambient conditions (fog, drizzle, slush etc.).
• ACC operates within certain driving speed ranges only (depending on model).
• Performance may be affected in small curve radii due to the
restricted visual range of the radar.
• ACC reacts to stationary objects.
• When driving through tunnels, the radar beams may reflect off
the tunnel walls. These reflections can potentially limit the
performance of the ACC system.
12
Description of ACC system
ACC options
The following overview shows the current Audi models (model year
2013) in which ACC is optionally available. A variety of system
configurations with model and country specific modifications are
used. The A6, A7 and A8* models generally come equipped with
two radar and transceiver units and two control units. An ACC
system with a control unit incl. a radar unit is used in the A3, A4,
A5, Q5 and Q7* models.
In the case of the A3, A4, A5 and Q5* models, ACC is also available
for vehicles with manual transmission.
In these models, ACC is available in 2nd gear and higher. After
selecting/changing gear and engaging the clutch, the accelerator
does not have to be depressed in order to activate ACC. It is not
possible to activate ACC while shifting gear.
The ACC systems used on Audi vehicles are joint developments of
AUDI AG and Robert Bosch AG.
*: including S models and RS models
Model
A3, S3
ACC version
**
A4, S4, RS4
A5, S5, RS5
A6, S6, RS6
***
A7, S7, RS7
A8, S8
Q5, SQ5
Q7
** ACC system with a control unit incl. a radar unit
(right adaptive cruise control sender G259 and ACC control unit J428)
*** ACC system with two control units incl. one radar unit each
(right adaptive cruise control sender G259 and ACC control unit J428 - masterleft adaptive cruise control sender G258 and ACC control unit 2 J850 -slave-)
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13
System parameters
Key system parameters for the functions of the ACC systems are
compared below.
1. Range and overlap angle
The range and overlap angle of the radar beams are dependent on
the type and number of radar transceiver units. In the case of the
A6, A7 and A8* models, the range at which the objects is still
reliably detected is approximately 200 m. In the A3, A4, A5, Q5
and Q7* models, this range is approximately 180 m. The detection
range starts approximately 0.5 m ahead of the vehicle.
The current systems utilise transceiver units with four transmitters/receivers whose beams partially overlap.
*: including S models and RS models
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620_019
Radar beams in vehicles with two transceiver units. (diagram of
Audi A8 from model year 2010) The overlap angle has been substantially increased by the double radar concept. Even 30 m ahead
of the vehicle, the detection range is already wider than a threelane motorway with a width of approximately 16 m.
14
This enables ACC to detect in advance vehicles entering its own
lane. ACC can, therefore, react proactively by initiating braking
operations and/or issuing warnings.
2. Control/speed range
The speed ranges within which ACC corrective adjustments are
permitted are dependent on model and country of use. The following speeds ranges* apply to the individual models:
A4, A5, Q5: ACC operates within the range from 30-200 kph.
Restrictions apply in some countries (30-150 kph).
A3: In this model, the speed range is dependent on the vehicle's
equipment level. If the vehicle is equipped with the driver assistance package (including front camera for driver assistance systems
R242), the speed range is also 30-200 kph. In vehicles equipped
with automatic transmission, corrective adjustments are made as
required until the vehicle comes to a stop. If the vehicle is not
equipped with the driver assistance package, the speed range is
30-150 kph.
Q7: ACC also operates within the speed range from
30-200 kph. Similarly, corrective adjustments are made as
required until the vehicle comes to a stop.
620_020
A6, A7, A8: The control range is 30-250 kph. Similarly, ACC makes
corrective adjustments as required until the vehicle comes to a
stop.
Restrictions apply in some countries (30-150 kph).
*: including S models and RS models
620_023
3. Object detection
The following rules regarding object detection by the radar sensors
apply to all ACC systems used in Audi models: ACC reacts to objects
which are moving or those which have already been identified as
moving objects. Although the system detects stationary objects,
its does not normally react to stationary vehicles, persons, animals
or oncoming traffic.
However, there are additional ACC functions which also factor
stationary objects into their corrective calculations.
An example of this is the Stop and go function which detects
obstacles between a stationary ACC-controlled vehicle and a
stationary vehicle ahead. In these cases, the automatic start
process is modified accordingly or is entirely suppressed after the
vehicle ahead drives away (see chapter on Stop and go function). In
these cases, the detection of stationary objects at close range is
assisted by additional sensors (camera, unltrasound sensors).
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15
System components
Vehicle overview
The diagram shows the Audi A8 together with all the control units involved in ACC control operations. These highly complex control operations involve 26 control units which exchange some 1600 units of information.
J104
J623
J387
J794
J852
J855
G85
J428
J743
J850
J519
J851
J527
16
J386
J389
J197
J393
J769
J773
J533
J770
J345
J540
J234
J388
J854
620_021
G85
J104
J197
J234
J345
J386
J387
J388
J389
J393
J428
J519
J527
Steering angle sender
ABS control unit
Adaptive suspension control unit
Airbag control unit
Trailer detector control unit
Driver's side door control unit
Door control unit, front passenger side
Door control unit, rear left
Door control unit, rear right
Convenience system central control unit
ACC control unit
Onboard power supply control unit
Steering column electronics control unit
J533
J540
J623
J743
J769
J770
J773
J794
J850
J851
J852
J854
J855
Data bus diagnostic interface
Electromechanical park and handbrake control unit
Engine management control unit
Mechatronics control unit
Lane change assist control unit
Audi side assist control unit 2
Convenience system central control unit 2
Information electronics control unit
ACC control unit 2
Image processing control unit
Camera control unit
Front left seat belt tensioner control unit
Front right seat belt tensioner control unit
17
ADR sender, right G259 and ACC control unit J428*
Left adaptive cruise control sender G258 and ACC control unit 2
J850 **
Mounting bracket
Layout:
The sender (radar transceiver) and control unit are installed in a
common housing (referred to hereinafter as the ACC unit). The
parts cannot be separated from one another and, if faulty, can only
be replaced as a complete unit at service centres. The unit is
mounted adjustably to a bracket and can be bolted to the vehicle
(bumper) along with the bracket.
A resistance heating wire is integrated in the lenticular cover.
*: Fitted in all vehicles with ACC
**: Only fitted in A6, S6, RS6, A7, S7, RS7, A8 and S8 models
620_025
Lens with integrated
heater ACC sender
Function:
The four radar sensors transmit continuous radar waves which are
bundled by the lenticular cover.
In most driving situations the integrated electrical heater prevents
the build-up of snow and ice, which have the effect of attenuating
the radar signals.
The radar signals received are evaluated by the control unit.
Basic function:
If the need for corrective action is detected, the desired distance to
a vehicle ahead is achieved by braking or accelerating. The following functions are utilised for this purpose:
• Active braking operations are initiated (by the ESC control unit
- or, in the Audi Q7, by the active brake servo).
• Engine torque is reduced or increased as required.
• In vehicles with automatic transmission, gearshifts are initiated
or suppressed.
Additional functions:
The additional functions are described in detail in the following
chapters.
18
620_026
The ACC control unit uses data bus systems to communicate with
the other control units. For this purpose, the ACC control unit is
connected to the data bus diagnostic interface (J533) by a special
data bus.
A master/slave configuration is implemented for ACC systems with
two transceiver units and two control units. Control unit J428 acts
as the master and control unit J850 as the slave.
620_027
ADR sender, right G259 and
ACC control unit J428
(master)
Left adaptive cruise control
sender G258 and ACC
control unit 2 J850
(slave)
ACC button E357
The stalk is located on the left-hand side of the steering column.
The switch positions are read in by the ACC control unit and the
corresponding system responses/settings are initiated.
620_023b
19
Networking - data transfer
The overview shows the system components which serve as as sensors and actuators for the ACC in the Audi A6, S6, RS6, A7, S7, RS7, A8
and S8 models. The key information received and transmitted by these components is summarised in note form under each component
designation.
Park assist steering control
unit J791
−− Front-side object detection
20
Instrument panel control unit
J285
−− Displays
Steering column electronics
control unit J527
−− Operation
(stalk signals)
Onboard power supply control
unit J519
−− Ambient temperature
−− Windscreen wiper actuation
Data bus diagnostic interface
J533
Convenience system
central control unit J393
−− Key operation
Engine management control
unit J623
−− Implementation of acceleration/deceleration
Trailer detector control unit
J345
Heater
Selector lever sensors J587
−− Selector lever position
Door control unit, driver side
J386
−− Door contacts
−− Bonnet
Gearbox control unit J217
−− Gearshifts
Front passenger door control
unit J387
Electromechanical park and
handbrake control unit J540
−− Stop management
Rear left door control unit
J388
Steering angle sender G85
−− Measured value for steering
angle
Rear right door control unit
J389
Airbag control unit J234
−− Crash status
−− Seat belt buckle status
Information electronics control
unit 1, J794
−− Settings
−− Navigation information
ACC control unit J428
−− Right wheel data:
−− ACC master function
Image processing control unit
J851
−− Front-side object detection
ACC control unit 2 J850
−− Left wheel data:
−− ACC slave function
Adaptive suspension control
unit J197
−− Damper adjustment for automatic emergency braking
Control unit for sensor electronics J849
−− Vehicle movement data (yaw
rate, transverse acceleration,
longitudinal acceleration)
ABS control unit J104
−− Implementation of vehicle
deceleration
Camera control unit J852
−− Vehicle lane data/course
Control unit for front right seat
belt tensioner J855
−− Belt tensioning
Control unit for front left seat
belt tensioner J854
−− Belt tensioning
Audi side assist control unit
J769
−− Rear-side object detection
Display and operation CAN bus
Convenience CAN bus
MOST bus
Audi side assist control unit 2
J770
Powertrain CAN bus
FlexRay
Extended CAN bus
620_028
21
Operation and driver information
This chapter covers the main aspects regarding operation of the
ACC systems and driver information displayed by the ACC systems.
This information is provided to give a better understanding of the
system as a whole and is no substitute for the Owner's Manual!
Detailed information can be found in the Owner's Manual for each
individual model.
620_024
The main operating functions are integrated in the stalk (ACC
button E357).
ACC on/off
The stalk has two locking positions. ACC is generally activated by
pulling the stalk towards the driver into the ON position. ACC is
deactivated by moving the stalk away from the driver into the OFF
position.
After starting the engine, ACC will, depending on the position of
the stalk, either be in READY mode (stalk in ON position) or in OFF
mode (stalk in OFF position).
After ACC is activated using the stalk, the system will also be in
READY mode. Once the target speed has been set, ACC enters
ACTIVE mode and corrective adjustments are made as required.
620_029
ACC OFF
When ACC is switched on, Electronic Stability Control (ESC) and
Electronic Traction Control are automatically activated if they have
previously been deactivated by the driver. Both systems cannot be
deactivated when ACC is switched on.
ACC ON
Setting the target speed
The current vehicle speed can be stored as a target speed by
pressing the SET button. A target speed can generally be set within
the given speed control ranges if the vehicle is travelling at 30 kph
or faster (see page 15). In vehicles equipped with the Stop and go
function, a target speed can be set even when travelling slower
than 30 kph. The vehicle is then accelerated up to 30 kph and the
target speed is set.
If the SET button is pressed in vehicles equipped with two ACC
units (see page 13) while travelling at speeds of greater than
250 kph, the vehicle is decelerated to 250 kph and then the target
speed is set.
The target speed can be increased by moving the stalk up and
reduced by moving the stalk down (in increments of 5 or 10 kph).
Increase speed
620_030
Reduce speed
Set speed
The actual target speed is indicated by LEDs in the speedometer
and briefly in the info line on the centre display after pressing the
SET button.
620_031
22
Setting the target distance
The desired distance to a vehicle ahead can be set in four stages
using the paddle. The factory default is distance setting 3.
The distance regulated by ACC is dependent on the speed at which
the vehicle is travelling. Vehicle-to-vehicle distance is increased
with increasing speed. The regulated distance is therefore not so
much constant distance as a time-constant distance. The current
distance setting is indicated on the centre display.
2
1
620_032
1 = reduce distance
2 = increase distance
Distance 1
Distance 2
Distance 3
Distance 4
Time interval 1.0 s
Time interval 1.3 s
Time interval 1.8 s
"Half speed indicated"
Time interval 2.3 s
Setting the drive program
In vehicles equipped with "Audi drive select", the drive program is
selected in "Audi drive select" and otherwise in the radio/MMI.
By selecting a certain drive program/driving mode, the driver can
influence the vehicle's acceleration and follow-up response during
ACC operation. The "comfort", "auto", "dynamic", "efficiency" and
"individual" settings can be selected. If a larger distance is
selected, the acceleration response will automatically be more
comfortable. The highest rate of acceleration is therefore achieved
by selecting distance 1 plus the "dynamic" drive program and the
lowest (most comfortable) by selecting distance 4 plus "comfort".
If "efficiency" is selected, the vehicle will be programmed for
maximum fuel economy with a relatively comfortable acceleration
response. If "individual" is selected, the acceleration response can
be freely selected by the driver in combination with other possible
system setups (engine, gearbox, steering etc.).
Audi drive select
Raise
Handbook
individual
efficiency
comfort
auto
dynamic
Set individual
Car systems
620_033
Raise
Audi drive select
Engine / gearbox
Air spring
Steering
Handbook
comfort
auto
Seat belt tensioners
comfort
auto
Adaptive cruise control
dynamic
Car systems
Set individual
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23
Setting the gong volume
Various system states are indicated to the driver audibly and
visually by a gong signal. In the A3, Q3, Q5, Q7 and A4/A5*
models, gong volume can be adapted to the driver input in the
radio/MMI. The "low", "medium" and "high" volume settings are
available for this purpose.
The audible signal can be muted by activating the "off" setting.
Even is the gong is switched off, for functional reasons not every
gong signal is deactivated.
In the current A6, A7 and A8* models, gong volume is adapted
automatically.
*: including S models and RS models
System status indication
The system status is indicated to the driver by indicator lamps and
via the centre display of the dash panel insert. The actual target
speed is indicated by the LED ring in the speedometer.
Refer to the Owner's Manual for details of possible displays.
Distance 2 - dynamic
620_034
How the driver is prompted to take over
To avoid unsettling the driver and for comfort reasons, the
maximum rate of brake deceleration usable to achieve the desired
vehicle-to-vehicle distance during automatic braking cycles is
limited to approximately 40 % of the maximum achievable rate of
brake deceleration in the ACC basic function. In certain situations,
this rate of brake deceleration will not be sufficient to achieve this
distance. In these cases, the driver must actively "assist". The
driver is prompted by audible and visual warnings to apply the
brake.
DISTANCE!
Basic operation
ACC is a driver assistance system. It was developed in order to
relieve the strain on the driver. Nevertheless the driver can exert
influence on the system at any time.
Active ACC corrective processes can be cancelled by applying the
brakes.
Similarly, the speed and acceleration set by ACC can be increased
by applying more throttle.
24
620_035
ACC auxiliary functions
Overview
ACC provides other auxiliary functions in addition to the basic
function. The range of functions is dependent on model and
country of use, and to a certain extent is tied to specific vehicle
equipment.
Function
Availability
Remarks
Audi braking guard*
Q7
Audi braking guard*
with automatic emergency braking
A3, S3, A4, S4, A5, S5, A6, S6, RS6 A7, S7, RS7
In the Audi A3, the functions of Audi braking
A8, S8, Q5, SQ5
guard are integrated in Audi pre sense.
Stop and go
A3, S3, A6, S6, RS6, A7, S7, RS7, A8, S8
With start-off monitoring and 15 s drive-away
readiness** in the A6, S6, RS6, A7, S7, RS7, A8
and S8, as well as 3 s drive-away readiness in the
A3 and S3.
Full deceleration at low
speeds
A3, S3, A4, S4, A5, S5, A6, S6, RS6, A7, S7, RS7,
Overtaking assistance
A3, S3, A4, S4, A5, S5, A6, S6, RS6, A7, S7, RS7,
A8, S8, Q5, SQ5
A8, S8, Q5, SQ5, Q7
Cornerning assistance
A6, S6, RS6, A7, S7, RS7, A8, S8
Overtaking prevention in
right driving lane
A3, S3, A4, S4, A5, S5, A6, S6, RS6, A7, S7, RS7
Lane change assistance
A6, S6, RS6, A7, S7, RS7, A8, S8
Boost function
A3, S3, A6, S6, RS6, A7, S7, RS7, A8, S8
A8, S8, Q5, SQ5
*: In future, the Audi braking guard functions in all models will be subfunctions of Audi pre sense.
Audi
**: The duration of start-off readiness can be extended in the Audi
A3, S3, A6, S6, RS6, A7, S7, RS7, A8 and S8 models by pressing the
stalk (see page 33/34).
Typical applications of Stop and go functions are tailbacks and slow-moving lines of traffic.
620_037
25
Audi braking guard
Audi braking guard alerts the driver to hazard situations. Typical
causes of such hazard situations are sudden heavy braking of the
vehicle ahead or if one's own vehicle approaches a much slowermoving vehicle ahead at high speed.
Failure to observe the necessary minimum distance to a vehicle
ahead is potentially very hazardous. Audi braking guard active even
if ACC has not been activated or is switched off.
Audi braking guard was implemented for the first time in an Audi
A6 in 2005. A hazardous situation is detected on the basis of radar
signals. If the vehicle is equipped with the front camera for driver
assistance systems R242 (implemented in the A3, S3, A6, S6, RS6,
A7, S7, RS7, A8 and S8 models), allowance is also made for video
information when evaluating the hazard potential of a driving
situation.
620_036
Audi braking guard subsequently implements the two warning
concepts explained below.
1. Distance warning
By evaluating the radar signals, Audi braking guard detects that for
a lengthy period of time the distance to a vehicle ahead is very
short (less than the distance realised after selecting distance 1). In
this case, heavy braking by the vehicle ahead could result in a
collision.
Audi braking guard assists the driver in this situation by issuing a
warning. A red-flashing warning lamp is activated in the display.
620_039
26
2. Forward collision warning (pre-warning)
The forward collision warning is activated when the distance to a
vehicle ahead decreases so rapidly that a collison can only be
avoided by taking evasive action or by applying heavy braking
outside the comfort zone. The driver must take immediate action.
In accordance with the high hazard potential of the situation,
warnings are issued visually by a warning lamp and in the centre
display, and audibly by a gong signal.
DISTANCE!
620_035
In these situations, it is important that the driver actively apply the
brakes in order to achieve high braking power (> 40 % of maximum
deceleration). If the driver does not react to the warning, the ACC
control unit initiates a short-term build-up of brake pressure
through the ESP control unit shortly before the last braking opportunity to a avoid collision.
This warning jerk can be clearly felt by the driver does not serve to
decelerate the vehicle but rather to again warn the driver that
immediate action must be taken to avoid an imminent collision.
V
t
+ gong
Pre-warning
!
620_041
Acute warning
by brake jerk
Preceding vehicle
brakes heavily - e.g. at the
end of a tailback
Information
Audi braking guard is active even if ACC is switched off.
27
If the driver does not respond to the acute warning (brake jerk),
the system assists by automatically initiating braking intervention.
In this section, the system responses ranging from a warning to
automatic emergency braking are shown in time sequence (phases
1-4).
In this example, an Audi A8 equipped with AAC and Audi pre sense
plus is approaching a much slower-moving truck. The other pre
sense functions (e.g. belt tensioners) mentioned in the given
example of the Audi A8 are dependent on the application in each
vehicle model.
620_040
Phase 1
The braking guard logic in the ACC control unit has detected an
increased collision risk and issues audible and visual warnings to
alert the driver. This warning is given if it is no longer possible to
brake comfortably or take evasive action to avoid a collision. When
exactly the warning is triggered depends on the driver's driving
style. Investigations have shown that the driving style also characterises the degree of driver alertness. For example, a dynamic
driving style characterised by frequent acceleration/deceleration
and lane changes generally infers an alert driver. The warning is
then triggered later than for a less alert driver. At this point, the
ESC system is instructed to pre-charge the brake system with
approximately 2 bar of brake pressure through the active build-up
of brake pressure. The purpose of this measure is to reduce the
delay times in the brake system in case braking is subsequently
applied. This measure initiates the cleaning/drying of the brake
discs by applying the brake pads against the brake discs. This
function is similar to the "brake disc wiper" function of the ESC
control unit.
At the same time, the triggering criteria for the Hydraulic Brake
Assist (HBA) are changed depending on the traffic situation around
the vehicle. Due to the high hazard potential of this situation, HBA
now deploys at lower brake pedal travel speeds. To be best prepared for any imminent dynamic actions (evasion, braking with
high vehicle deceleration), the sdaptive air suspension (aas) sets
the dampers to maximum damping force.
DISTANCE!
620_035
620_042
28
Phase 2
If the driver does not react to the pre-warning, the ACC control unit
initiates a short-term brake pressure build-up (which is felt by the
driver as clear brake jerk) before the last braking opportunity to
avoid a collision. The sole purpose of this brake jerk is to again
urgently warn the driver that it is necessary to take immediate
action (evasive action, braking). If the driver thereupon initiates
emergency braking by rapidly depressing the brake pedal, he will,
if necessary, be assisted by Hydraulic Brake Assist (HBA). The
response thresholds of HBA have already been lowered during
phase 1 depending on the hazard potential of the situation. If the
driver but does not apply sufficient foot pressure to the brake
pedal to achieve the necessary rate of deceleration calculated by
the system, ESC will initiate additional brake pressure as required.
The built-up braking pressure either stops the vehicle a short
distance behind the vehicle ahead or vehicle speed is reduced to
such an extent that it can safely follow the preceding vehicle.
Depending on road conditions, maximum deceleration values are
initiated if necessary.
• Brake jerk
• Partial braking (approximately 30 %)
• Seat belt slack reduction
620_043
If the driver does not respond to the brake jerk by applying the
brake, ACC will initiate automatic braking through ESC. The first
phase of brake pressure build-up begins with medium deceleration
(approximately 30 % of maximum deceleration for approximately1.5 s). Seat belt slack is reduced at the start of the automatic braking operation by Audi pre sense in order to effectively
restrain the driver.
The following phases 3 and 4 are initiated only in vehicles equipped with Audi side assist (which becomes Audi pre sense plus when combined with ACC). The driver can cancel the corresponding function any time by firmly depressing the brake or accelerator pedal or by taking
evasive action.
Phase 3
Brake pressure is reduced to approximately 50 % of maximum
deceleration by ESC. Following traffic is alerted to the hazard situation by emergency flashers. Given the high likelihood of a collision,
open windows/sunroof are closed as far as possible by Audi pre
sense. The object is to increase the stability of the passenger cell
and protect the occupants from object intrusion.
• Partial braking (approximately 50 %)
• Closing windows/sunroof
• Hazard warning flashing
620_044
29
Phase 4
If the driver still fails to take action and a collision at a high residual speed can no longer be avoided, the brake pressure will again
be increased to the maximum rate of deceleration shortly before
the calculated point of impact. Audi pre sense additionally activates the belt tensioners. The collision can no longer be prevented
by the driver but the collision speed can be reduced by up to about
12 kph by applying maximum braking power. Even if the driver
takes no evasive action, Audi braking guard can reduce the impact
speed by up to 40 kph. The accident cannot be prevented without
intervention by the driver, but its severity is significantly reduced
by Audi braking guard.
• Emergency braking
• Seat belt pretensioner activation
620_045
Unlike the ACC basic function, Audi braking guard also reacts to
stationary targets. In these cases, the driver is alerted by audible
and visual warnings and, if necessary, by a warning jerk as
described. However, automatic braking is not performed at speeds
above 30 kph. Depending on model, the "full deceleration at low
speeds" function is activated at speeds below 30 kph (see overview
on page 25).
Audi braking guard can be deactivated by the driver as a complete
system.
Alternatively, it is possible to deactivate only the distance and collision warning functions.
Raise
Handbook
Driver assist
When ESC sport mode or offroad mode is activated, Audi braking
guard is also deactivated.
Audi braking guard
System
On
Pre-warning
On
Car systems
Set individual
620_046
In the Audi A3 from model year 2013 and later, the Audi braking
guard functions are included in the functional range of Audi pre
sense. This concept will in future be implemented in all Audi
models. As with Audi braking guard, it is possible to deactivate
Audi pre sense as a complete system or to deactivate the distance
and collision warning functions only.
Car
Handbook
Audi pre sense
System
Pre-warning
The Audi pre sense functions are partially deactivated when ESC
sport mode is activated (or the Offroad mode in later Q models).
CAR systems
620_047
30
Evolution
The Audi braking guard function has grown in complexity over the
course of its evolution. The following chapter shows the developmental phases and functions of Audi braking guard in chronological order.
Audi braking guard 1
Installed in A6 from MY 2005
− Pre-charging of the brake system by
ESC in the event of a collision hazard
− without warning the driver
− Reduction of intervention threshold of
Hydraulic Brake Assist (HBA)
2005
Audi braking guard 2 with pre sense front/plus
Installed in A8 from MY 2010
A6 and A7 from MY 2011
− Pre-charging of the brake system by ESC in the
event of a collision hazard
− Distance warning by warning lamp
− Audible and visual collision warnings
− Acute warning by brake jerk
− Automatic partial braking if driver ignores warnings
− Automatic emergency braking shortly before
collision (only if vehicle is equipped with pre sense rear)
− Reduced intervention threshold of Hydraulic Brake Assist
(HBA)
2010
2007
Audi braking guard 2
Installed in Q7 and A5 from MY 2007
A4 and Q5 from MY 2008
− Pre-charging of the brake system by ESC in
the event of a collision hazard
− Distance warning by warning lamp
− Audible and visual collision warnings
− Acute warning by brake jerk
− Reduced intervention threshold of Hydraulic
Brake Assist (HBA)
2013
2012
Model year
Audi braking guard 2 with pre sense and maximum deceleration at low speeds
Installed in A4, A5, A6, A7 and A8 (phased in from MY 2012)
A3 and Q5 from MY 2013 and later
− Functions such as Audi braking guard 2 with pre sense front/
plus
− Automatic emergency braking at speeds of less than 30 kph
31
Audi Stop and go
In the current Audi A3, S3, A6, S6, RS6, A7, S7, RS7, A8 and S8
models, the Stop and go function is implemented on vehicles
equipped with ACC.
As previously with ACC in the Q7, the above vehicles also brake to a
stop automatically. A precondition for this is that the vehicle ahead
was moving before it came to a stop. Targets that are stationary at
the point of detection are not included in the control function (e.g.
parked vehicles).
If ACC registers that the vehicle ahead has come to a stop, the
ACC-equipped vehicle is also automatically braked to a stop
without any action on the part of the driver. The rate of deceleration is dependent on the vehicle speed. At vehicle speeds of less
than 50 kph, the maximum rate of deceleration is approximately 4
m/s2. The last 2-3 m before the vehicle comes to a stop are covered
by "crawling" at a speed of approximately 2 kph. The stopping
distance to the vehicle ahead is approximately 3.5 - 4 m.
If the vehicle ahead starts off again after stopping briefly, the
ACC-equipped vehicle will also accelerate and follow. The braking
operations necessary to implement this function are performed by
the "brake pressure build-up" function of the ESC.
620_049
The duration of start-off readiness is model-dependent and can be
extended by a set amount using the stalk (RESUME position).
620_023b
If ACC has brought the vehicle to a stop by an active braking
operation, the electrical parking brake is automatically activated
and ACC is deactivated in the following situations:
• The vehicle is stationary for longer than 3 min
• Opening the driver's door
• System fault
• In the case of the Audi A3 and S3 models, ACC is deactivated if
the driver's seat belt is unfastened while the vehicle is stationary. In the case of the Audi A6, S6, RS6, A7, S7, RS7, A8 and S8
models, the vehicle will no longer start off automatically.
620_050
!
32
Information
In certain markets (e.g., USA) ), the vehicle executes a "stop" but does not automatically "go". To move off again, the driver
must activate ACC with the stalk (RESUME) or by depressing the accelerator.
ACC-equipped vehicle starts off automatically
Preceding vehicle starts off again
Driver operates stalk
ACC-equipped vehicle brakes to standstill
Preceding vehicle stops
Preceding
vehicle
Stationary
Moving
ACC-equipped vehicle
Stationary
Moving
State
ACC ready
Not ready
State
Vehicles
ACC system
Max. duration 15 s
Operation
Displays
RESUME
Operated
Not operated
Text
ACC: ready
No display
ACC symbol
Shown
Not shown
Example showing the time sequence of the control operations of an Audi A8 in Stop and go mode.
Time t
620_051
ACC READY is indicated to the driver in the central display. The
precondition for starting off is that the driver has fastened his seat
belt.
In certain markets, the automatic start-off function is realised
without the described option of extending the READY period with
the stalk.
Distance 2 - dynamic
ACC: rreadyready
620_038
33
Start-off monitoring in Audi A6, S6, RS6, A7, S7,
RS7, A8 and S8
Before the ACC-equipped vehicle starts off automatically, the ACC
scans the area between the ACC-equipped vehicle and the vehicle
ahead. Audible and visual warnings are given if an obstacle is
detected. The vehicle nevertheless commences the drive-away
cycle, but starts off but very slowly. This gives the driver sufficient
time to respond by braking or taking evasive action.
The area in front of the vehicle is monitored by three independent
systems: the radar sensors, video camera R242 and the ultrasonic
sensors of the parking aid. If the vehicle is equipped with ACC, the
ultrasonic sensors are operated in a different mode so that objects
are still detected at a distance of approximately 4 m.
If the signal from the video camera or the ultrasonic sensors is
unavailable, the vehicle will always start off automatically at a
reduced rate of acceleration. Automatic start-off is suppressed if
both signals are unavailable. The system is then deactivated and
the driver is requested to take over.
620_053
In the Audi A3 and S3, drive-away readiness is limited by "RESUME"
to 3 s (in the Audi A6, S6, RS6, A7, S7, RS7, A8 and S8, this is 15
s). Because this duration is so short, the Audi A3 and S3 models do
not have a special start-off monitoring function.
Hill Start Assist in combination with Audi Stop and go
Stop and go can also be combined with Hill Start Assist. The drive
assist function can be activated/deactivated independently of the
ACC at any time.
If Hill Start Assist and Audi Stop and go are active while the vehicle
is stationary, the Hill Start assist function will switch passively into
the background (comparable to "standby" mode).
If ACC is switched off while the vehicle is stationary and Hill Start
Assist is on, Hill Start Assist is re-activated and holds the vehicle
stationary.
620_054
!
34
Information
Automatic restarting can be deactivated using the diagnostic tester.
Full deceleration at low speeds
Overtaking assistance
This function was first introduced in the Audi A4, A7 and A8
models from model year 2012. The vehicle is braked automatically
when a risk of collision exists at low vehicle speeds under 30 kph.
The data collected by the ACC is the basis for detection of the
collision risk. In the case of the A6, S6, RS6, A7, S7, RS7, A8 and
S8 models, the video information from camera R242 is factored in
when evaluating the hazard potential. This assessment is made by
specific software on the ACC control unit. The control unit then
"instructs" the ESC control unit to brake the vehicle by indicating a
nominal rate of deceleration (approximately -8 m/s2). The ESC
control unit then initiates the build-up of brake pressure at all four
wheel brakes.
This function facilitates rapid overtaking manoeuvres. When a turn
signal is activated, the ACC interprets that the driver wishes to
overtake. The vehicle is then accelerated before leaving its lane and
until the overtaking maneouvre is complete. This is essentially how
a driver would behave during "normal" driving. The function is
activated in a situation-dependent way.
620_055
620_056
Cornerning assistance
Control behaviour when cornering
ACC utilises the predictive route data of the navigation system to
perform this function. If a corner is detected in the road ahead,
ACC computes the speed at which this corner can be safely taken.
Cornering assist will be activated if the vehicle's current speed
exceeds the nominal speed computed by ACC. The vehicle's speed
is reduced by up to
10-15 kph on entering the corner by reducing the drive torque
(utilisation of engine drag torque).
If ACC detects that a vehicle's transverse acceleration exceeds a
calculated nominal value, the vehicle's speed is reduced accordingly.
In this example, the set target speed is 120 kph and the vehicle
takes a corner with a clear road ahead, i.e. the vehicle does not
have to maintain a target distance to a slower-moving vehicle
ahead. While the vehicle is rounding the corner, the ACC control
unit computes a nominal speed of 110 kph based on the measured
transverse acceleration. The vehicle's speed is then limited to110
kph by reducing the drive torque.
Allowance if made for trailer operation and the selected driving
program when determining the nominal speed.
620_057
620_052
35
Overtaking prevention in right driving lane
If ACC mode is active and the road ahead is clear, overtaking/
passing in the right driving lane is only possible without restrictions up to a defined vehicle speed. It is only possible to pass a
vehicle at a limited relative speed of approx 10 kph.
The function is now active and does not allow overtaking/passing
in the right lane. The active function can be cancelled at any time
by accelerating manually with the stalk (RESUME), by depressing
the accelerator pedal or by increasing the set speed.
Driving speed
V2
V1
620_058
Unrestricted overtaking on the right
(up to speed V1)
Overtaking on the right is only possible at a limited relative speed
(up to speed V2)
Overtaking on the right is not possible
(at speed V2 or higher)
620_059
36
Lane change assistance
To realise this function, the vehicle must be equipped with Audi
side assist and camera R242. Braking intervention is adapted to
the following traffic and the oncoming traffic in the overtaking
lane.
The camera detects the lane markings. Two typical driving situations will now be used to explain how ACC works.
620_060
Driving situation 1
The ACC-equipped vehicle is rapidly approaching a slower-moving
vehicle ahead and the driver operates the turn signal to indicate
that he wishes to change lane. The rear radar sensor indicates to
Audi side assist that the left lane behind the vehicle is clear. Also,
ACC detects no vehicle in the left lane ahead of the ACC-equipped
vehicle. The camera identifies the broken lane markings. ACC
derives the following information from the input signals:
• It is safe to overtake because there is no subsequent traffic in
the left lane.
• The lane change can be performed without reducing speed
because there is no other vehicle ahead in the overtaking lane.
• Broken lane markings mean overtaking is permitted. There is a
high likelihood that the driver will perform the overtaking
manoeuvre.
When the set target distance is achieved, ACC does not brake
the vehicle to the speed which it would otherwise set when
following a vehicle in front without performing an overtaking
manoeuvre. This means that the lane change can be performed
much more smoothly and comfortably.
37
Driving situation 2
The ACC-equipped vehicle is rapidly approaching a slower-moving
vehicle ahead and the driver operates the turn signals to indicate
that he wishes to change lane. The rear radar sensor indicates to
Audi side assist that the left lane behind the vehicle is busy. ACC
also detects a vehicle in the left lane ahead of the ACC-equipped
vehicle. The camera identifies the broken lane markings. ACC
derives the following information from the input signals:
• It is only to a limited degree safe to overtake because there is
subsequent traffic in the left lane.
• The lane change cannot be performed without reducing speed
because there is another vehicle ahead in the overtaking lane.
• Broken lane markings mean overtaking is permitted. There is a
high likelihood that the driver will perform the overtaking
manoeuvre.
When the set target distance is achieved, ACC brakes the vehicle
to a lower speed than in the above example. The speeds of the
vehicles driving in the left lane are taken into account when
determining the required amount of corrective braking.
620_061
If the camera detects solid lane markings, a lane change is
assessed as improbable and the braking interventions are executed
as they would be when driving in lane without changing lane.
Boost function
The boost function enables the driver to increase the driving speed
currently set by ACC without having to deactivate ACC. This is
achieved by depressing the accelerator pedal or by pulling the
stalk. If the boost function is no longer required, ACC slows down
again to the originally set speed.
620_063
38
Service operations
The most common service operations are briefly explained in this
chapter.
The ACC systems (ADR sender, right G259 and ACC control unit
J428/left adaptive cruise control sender G258 and ACC control unit
2 J850) have full self-diagnostic capability.
Detected events are stored in the vehicle's event memory at
diagnosis address 13 / 8B together with details of the ambient
conditions in each case.
Corresponding fault finding programs are linked to the entries in
the event memory.
Sensor vision
Despite the "robust" propagation characteristics of the radar beam,
ACC may be deactivated due to impaired conditions of "visibility".
This can happen for various reasons.
• The propagation of the radar beam is significantly impaired by
the weather conditions. This is possible in spray, fog and snow.
This can only be remedied by an improvement in the weather
conditions.
ACC and
Audi braking guard:
currently unavailable
No sensor vision
• The lens on the radar sensor is dirty. After the lens has been
cleaned, ACC will again be available. Commercially available
cleaning agents can generally be used for cleaning all motor
vehicles.
• The vehicle is operated in a region where very few objects are
definable by the ACC as targets. This is rarely the case, e.g.
when driving through desert-like regions.
620_064
• When passing through tunnels, signal reflection off the tunnel
walls may lead to deactivation of the ACC.
Replacement and removal/installation of
the ACC sender with ACC control unit
In the event of a fault in the sender or control unit, the complete
ACC unit must always be replaced. It is not permitted to separate
both components. It is necessary to calibrate the sender after
installing the ACC unit.
620_025
!
Information
It is important that basic setting of the stud length be correctly performed prior to installation of the ACC unit. Refer to the
workshop manual for detailed information.
39
Calibrating the ACC sender
To ensure precise operation, the sender(s) must be exactly calibrated. Only then can a vehicle driving ahead in the same lane be
identified as a relevant vehicle.
If the sender is not set precisely in the horizontal direction, the
system may incorrectly react to vehicles driving in the adjacent
lanes.
620_066
The bumpers of the Audi A8 have been replaced. The senders have
been installed without subsequently being calibrated. By incorrectly aligning with the left lane, ACC now controls the distance to
the passenger car driving in this lane and not the truck in the same
lane.
This unwanted control behaviour is even more noticeable when
cornerning, particularly in the left hand corners in this example.
The sender must be calibrated if:
In vehicles equipped with two ACC units (ADR sender, right G259
and ACC control unit J428 as well as left adaptive cruise control
sender G258 and ACC control unit 2 J850), both senders must
always be set. The setting procedure should begin with sender
G259, which acts as the master.
• the rear axle tracking has been adjusted.
• the ACC unit (sender and control unit) have been removed and
installed.
• the front bumper has been removed and installed.
• the front bumper has been loosened or displaced.
• the front bumper has been damaged by the application of
excessive force to the bumper.
• the horizontal misalignment angle is outside the range -0.8° to
+0.8°.
ADR sender, right G259 and
ACC control unit J428
(master)
Left adaptive cruise control
sender G258 and ACC
control unit 2 J850
(slave)
620_027a
40
The ACC unit is attached to the baseplate by three studs. The
baseplate is rigidly bolted to the bumper. The studs are tipped with
ball heads. The ball heads are mounted in plastic ball joint sockets
fitted into mounting eyelets in the baseplate. The screw threads
are inserted in plastic elements on the sender (clips). Two of the
three screws (A,B) are for setting the sender; the third screw (C) is
non-adjustably attached to the sender housing.
Turning the screws (A or B) adjusts the distance between the
sender and the baseplate. The sender is pivoted about the axis
formed by the non-adjustable screw (C) and by the second, adjustable screw (B or A). This allows the senders to be adjusted independently in the horizontal direction (red axis) and in the vertical
direction (blue axis). This adjustment (turning of the screws) can
be made using the setting tool VAS 6190/2.
620_068
1
2
3
1 = plastic ball joint sockets
2 = mounting bracket
3 = cover
4 = stud
5 = clip
6 = ACC sender and ACC control unit
4
5
6
620_067
A prerequisite for successful calibration of the ACC sender is that
the stud length is correctly set.
620_065
41
A sender can be calibrated using the following special tools:
• VAS 6190A (not suitable for A6, S6, RS6, A7, S7, RS7, A8 and
S8, no longer included in workshop equipment range)
• ACC setting device VAS 6430
or
setting device, basic set VAS 6430/1 together with ACC reflector mirror VAS 6430/3
620_069
The basic principle of the calibration procedure is the same irrespective of ACC system and vehicle model:
A mirror is positioned in front of the vehicle at right angles to the
vehicle's geometric driving axis (the geometric driving axis indicates the running direction of the rear axle and, thus, the vehicle's
direction of motion when driving in a straight line). Exact positioning of the mirror necessitates the use of an axle alignment stand
and initial alignment of the vehicle.
To determine whether the position of the radar sensor is within the
nominal range, a full vehicle alignment procedure must be performed. A "quick-entry" wheel alignment procedure is sufficient
(performance of rim runout compensation together with alignment of the rear axle track width).
!
The radar sensors are then instructed by the ACC control unit to
transmit radar waves and receive the waves reflected by the mirror.
The mechanic initiates this procedure using the diagnostic tester.
The sender is set correctly if the reflected radar waves impinge on
the ACC control unit in exactly the same position from which they
originated. The control unit evaluates the extent of the deviation
from the point of origin and thereby determines the misalignment
angle. The diagnostic tester tells the mechanic what adjustment to
make at the relevant setting screw.
Information
A key requirement for an exact adjustment is the careful alignment of the mirror perpendicular to the geometric driving axis.
If this setting is not made correctly, the remainder of the setting procedure will go smoothly but the sender will still exhibit
too large a misalignment angle after the calibration has been completed.
620_070
42
ACC transmits and receives signals after it is initialised following
engine start-up. The ACC system permanently transmits and
receives signals during the subsequent driving cycle (after terminal
15 "on") even if the driver has not activated the system. Even
during subsequent stop cycles in vehicles equipped with the Start
Stop System, ACC continues to transmit and receive signals.
The system detects a misalignment of the sender by evaluating the
following key information:
Forces acting directly on the peripheral regions of the ACC unit may
be sufficient to force the ball head tips of the studs out of the ball
joint sockets in the mounting bracket. This can, for example, occur
in the winter if the bumper is driven into a snow bank when
parking the vehicle. In these cases, the misalignment angle will be
sufficiently large to initiate system deactivation. In most cases,
subsequent calibration efforts will prove unsuccessful. This is why
it is important to always check that the sender is properly attached
before it is calibrated.
• objects detected by ACC (crash barriers, other vehicles)
• yaw rate (vehicle movement about the vehicle's vertical axis)
The measured value for horizontal misalignment angle, which can
be read out using the diagnostic tester, is important information
that allows service centres to assess the system's behaviour. Even
deviations in the order of approximately 0.8° are very noticeable in
the control behaviour of the system and should be corrected by
calibrating the sender at a qualified service centre. If the deviation
exceeds approximately 1.4°, the system will be shut down and an
entry will be made in the vehicle's event memory.
l The misalignment angle of ACC
control unit 1 (J428) is currently 0.048°
l The misalignment angle of ACC
control unit 2 (J850) is currently 0.26°
Calibration is not necessary until a misalignment angle
of 0.8° is exceeded.
Should ACC control units (J428 and J850) still be
re-calibrated?
Help
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