SSP_960393

Active suspension
eSelf Study Program 960393
Audi of America, LLC
Service Training
Created in the U.S.A.
Created 2/2020
Course Number 960393
©2020 Audi of America, LLC
All rights reserved. Information contained in this manual is based on the
latest information available at the time of printing and is subject to the
copyright and other intellectual property rights of Audi of America, LLC.,
its affiliated companies and its licensors. All rights are reserved to make
changes at any time without notice. No part of this document may be
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referred to Audi of America, LLC.
Always check Technical Bulletins and the latest electronic service repair
literature for information that may supersede any information included in
this booklet.
The eSelf-Study Program (eSSP) teaches a basic understanding 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.
For further information about maintenance and repair work, always refer to the current technical literature.
Release: February 2020
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Introduction
Running gear concepts compared 
Basic principle
Design of the system 
System components
Actuators for running gear stabilization 
Harmonic drive gear 
Electric motor 
Suspension stabilization control modules 
Drivetrain Control Module J775 
System functions
Additional
Additional
Additional
Additional
Additional
preview function 
crash lifting function 
elevated entry function 
corner tilting function 
helicopter function 
Operation and servicing
Operation and driver information 
System behavior in the event of a fault 
Service operations 
Knowledge assessment
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Introduction
The Audi active suspension is an electromechanically operated suspension system. It can increase or reduce the load
on each wheel individually to adjust to the road as needed.
This means the system can actively control the position of
the vehicle body in every driving situation.
For each wheel there is one electric motor supplied by a
48-volt electrical system. The Driver Assistance Systems
Control Module sends control signals to the active suspension every five milliseconds. A single Suspension Stabilization Control Module per axle processes the signals for the
electric motors. A belt drive and compact gearing arrangement step up the torque of the electric motor and transfer it
to a steel rotary tube. The tube houses and is rigidly joined
to a titanium torsion bar. This bar is more than 15.7 in
(40 cm) long, approximately 0.9 in (22 mm) thick and,
despite its high strength, can be twisted more than 20
degrees. The force is transferred from the end of the torsion
bar to the suspension via a lever and a coupling rod. This
force is exerted at the front axle on the pneumatic strut of
the adaptive air suspension and at the rear axle, on the
transverse link.
The range of ride characteristics takes on a whole new
dimension thanks to the flexibility of the active suspension.
If the driver chooses “Dynamic” mode in the Audi drive
select system, the car becomes a sports car. It turns firmly
into corners and body roll angles are reduced by half compared with a conventional suspension. The body hardly dives
at all during braking. In “Comfort” mode, however, it glides
smoothly over any and all road surface irregularities. The
active suspension settles the superstructure by continuously
adding energy to or removing energy from the body depending on the respective driving situation.
The active suspension also enhances passive safety. The
system uses the sensors networked in the Driver Assistance
Systems Control Module (zFAS) to detect risks of a collision
around the vehicle. In the event of an imminent side impact
of more than 15.5 mph (25 km/h), the suspension actuators
raise the body on the exposed side by up to 3.1 in (80 mm)
within half a second. As a result, the collision is directed to
the even stronger areas of the vehicle, such as side sills and
floor structure. The load on occupants is reduced by up to 50
percent compared with a side impact when the body is not
raised.
677_008_03
677_001
4
Running gear concepts compared
Conventional running gear
Springs, dampers and anti-roll bars for conventionally
constructed axles are designed to the special conditions for
which the vehicle is used. These systems, which cannot
change when the vehicle is moving, are always a compromise. The usage possibilities of the vehicle are limited.
In addition, there is a conflict between designing the components with a focus on dynamic driving or on comfort.
Running gear designed for sporty driving cannot offer the
comfort which can be provided by running gear designed
for comfort.
Front axle of conventional, non-regulated running gear
Conversely, a vehicle with running gear designed for
comfort will not be able to offer the driving dynamics which
can be offered by a sporty design. Furthermore, the
self-steering behavior of the vehicle is defined by the relation between the fixed anti-roll bar rigidities on the front
and rear axles. Depending on the design of the anti-roll
bars, the vehicle will understeer, oversteer or handle
almost neutrally when driven on the limit.
In the past, springs with progressive rates were used along
with dampers on which the damping characteristics
changed depending on the spring travel. However, this also
meant no opportunity to react to external conditions or the
driver’s wishes via a targeted adjustment of the spring and
damping forces.
677_002
5
Adaptive air suspension
To deal with the compromises of conventional running
gear, dampers with the capability of adjustment while the
vehicle is moving can be used.
Using air springs instead of steel springs also allows for
regulation of the vehicle ride height. Corresponding sensors
record dynamic driving parameters such as vehicle speed,
accelerations and torques. The damping forces are adjusted
to the situation depending on the dynamic driving conditions. The driver can also choose between sporty, balanced
and comfortable handling by selecting specific driving
programs which activate specific characteristic maps.
Thanks to the option of changing the volume of air in the
air springs, different vehicle ride heights can be achieved. If
the vehicle ride height remains the same, changes to the
vehicle’s load cause corresponding changes to the air pressure in the air springs. The natural frequency of the vehicle
body remains almost exactly the same as a result, irrespective of the load. As a result, the driver does not notice any
significant changes to vehicle comfort and driving dynamics, even if the load is changed.
Because air is compressible, a short amount of time is
needed between when the pump starts delivering and an
increase in volume in the air springs can be measured.
Therefore, changes to the vehicle level/vertical forces
cannot occur in real time. Furthermore, it is not possible to
initiate forces in the opposite direction; that is to have the
wheel “pull” on the vehicle body.
677_003
Front axle of regulated running gear with air suspension and damping control (adaptive air suspension)
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Adaptive air suspension with Electromechanical Roll Stabilization (ERS)
This system was offered for the first time as an option in
the Audi SQ7 in other markets. With the use of
electromechanical control elements, the torsional rigidity
of the anti-roll bars on the front and rear axles can be
varied separately. The control elements connect the antiroll bar “halves” on one axle and tension them against
each other with correspondingly regulated forces. As a
result, it is possible to increase the support provided by
the outer wheels in corners, which effectively restricts the
roll inclination of the vehicle body.
In addition, the self-steering behavior of the vehicle is
affected by achieving a defined relation between the antiroll bar rigidities on the front and rear axles.
The force-transmitting connection between the wheels on
an axle via the anti-roll bar can be reduced to a minimum,
but the application of forces via a corresponding rigidity
change always occurs alternately on both wheels of an axle
at the same time.
Sway Stabilization
Control Module
J924
“Anti-roll bar half” permanently
connected to the actuator
Left Front Suspension
Stabilization Actuator
V634
“Anti-roll bar half” bolted to the
actuator - non-detachable connection
Front axle of the Audi SQ7 with Electromechanical Roll Stabilization (ERS)
677_004
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Vehicles with active suspension
The active suspension is an electromechanical suspension
system. With this system, four separate vertical forces per
wheel plus their direction can be set between the vehicle
body and the wheels.
As a result, the wheels on a single axle are no longer
coupled (as on the ERS system) and the corresponding
application of identical (opposing) forces on both wheels
no longer occurs. Force can be applied to a wheel without
affecting the other wheel on the corresponding axle.
In addition, the vertical forces can be applied in both
directions, therefore making it possible for the vehicle body
to be “pulled” in the direction of the road by the wheels.
This method of applying force to all four wheels separately
provides additional new options for influencing driving
dynamics and comfort.
Audi A8 with active suspension
8
The active suspension combines the following functions:
›
›
›
›
Active roll stabilization.
Active pitch stabilization.
Active vertical body control.
Dynamic height adjustment
(elevated entry function, crash lifting function).
The “classic” conflict between driving comfort and dynamic
driving is resolved with the active suspension. The driver
experiences a vehicle with the dynamics of a sports car and
the comfort of the luxury class.
677_005
The illustration below compares the driving dynamics and
comfort characteristics of the adaptive air suspension
(AAS, red) with those of the electromechanical active roll
stabilization (ERS, yellow), the Active suspension basic
system (green) and the Active suspension basic system
with additional functions (blue).
By selecting the desired driving program in Audi drive
select, the driver can decide whether to prioritize driving
dynamics (sportiness) or to drive more comfortably. This is
made possible by the system-specific spread which is also
illustrated in the diagram.
Driving dynamics
The adaptive air suspension was used as the reference.
Spread due to Audi drive
select setting chosen
Driving comfort
677_006
Key:
AAS (Adaptive air suspension)
AAS + ERS (Adaptive air suspension + ERS [active roll stabilization])
Active suspension (basic system)
Active suspension (basic system)+ additional functions
Audi drive select setting “auto”
Audi drive select setting “dynamic”
Audi drive select setting “comfort”
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Basic principle
Design of the system
The principle of the active suspension system can be
depicted using the electromechanical roll stabilization as a
basis. On the roll stabilization system, the anti-roll bar is
divided into two components, approximately in the center.
The two components are connected by an electromechanical actuator. This actuator tensions the two components
against each other, which causes the torsional torque and
therefore also the vertical forces which act on the axles of
the vehicle body to increase as the tension increases.
Compared with a hydraulic system, the electric actuation
also significantly reduces the energy required, in addition
to many other benefits. The electric motors are activated by
a single Suspension Stabilization Control Module per axle.
Drivetrain Control Module J775 activates the two control
modules via a sub-bus.
To regulate individual wheels, the two “halves” of the
anti-roll bar on the active suspension are not connected
and tensioned against each other. Each “half” of the antiroll bar is tensioned by a separate actuator. The actuators
are driven by electric motors.
Adaptive suspension with ERS
ERS actuator to tension
the torsion bar halves
Active suspension
Separate actuators to
twist the torsion bars
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677_008
Suspension Stabilization
Control Module 1
J1152
Drivetrain Control Module
J775
Suspension Stabilization
Control Module 2 J1153
677_009
J775 calculates the regulating inputs required at the front
and rear axles. The two chassis stabilization control
modules implement the specifications by activating the
electric motors on the front and rear axles for each wheel
individually.
The actuators are bolted to the vehicle underbody (bodymounted) together with the subframes for the front and
rear axles. When an actuator is operated, the lever which it
actuates turns. A coupling rod connected to the end of the
lever is connected to the damper stalk on the front axle and
the transverse link on the rear axle.
Because of the turning movement of the lever, a vertical
force component acts on the corresponding damper stalk
or the corresponding transverse link via the relevant coupling rod. As a result, the distance between the wheel and
the vehicle body is reduced or increased depending on the
direction in which the actuator is turning (springs moving
up or down).
Front Suspension
Stabilization Actuator
677_011
Front Suspension
Stabilization Actuator
677_012
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The illustration below shows the activation of a front axle
actuator as an example. The actuator lever is connected to
the damper stalk via the coupling rod. The actuator supports
itself on the wheel contact point via the lever, coupling rod,
damper stalk and transverse link. The turning movement of
the lever illustrated (shown in red) causes the actuator and
the vehicle body directly connected to it to be raised.
The piston rod of the damper is put under tension (rebound
damping). If the lever is turned in the opposite direction,
the vehicle body is lowered. The suspension strut
compresses and the piston rod of the damper is put under
load (compression damping).
677_010
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System components
Actuators for running gear stabilization
Design
The coupling rod is connected to the upper bearing at the
damper stalk of the front axle damper and at the top transverse links of the rear axle. The lower bearing of the coupling
rod is connected to a lever. The end of the lever is form-fit to
the torsion bar. The other end of the torsion bar is form-fit
to the end of the torque tube.
The torque tube forms the extension of the output of the
harmonic drive gear (strain wave gearing). The input shaft
of this gearing is connected to the rotor of the electric
motor via a toothed belt. The power is transmitted from
the electric motor via the toothed belt to the harmonic
drive gear, where it is output to the coupling rod via the
torque tube, torsion bar and lever.
Upper bearing for
connection to
damper stalk
Coupling rod
Lever
Form-fit
Harmonic drive
gear
Form-fit
Electric
motor
Toothed
belt
Torsion bar
Torque tube
677_013
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Function
The actuator provides a torque of approximately 811.3 lb-ft
(1,100 Nm) at the drive gear output; the maximum force at
the coupling rods is approximately 1124.40 lb (5.0 kN) on
the front axle and approximately 1011.65 lb (4.5 kN) on
the rear axle.
Lever angles of +/- 42° can be set from the zero position.
The body can be raised by approximately 3.34 in (85 mm)
from the center position at all four corners in just five
tenths of a second.
F
E
B
A
D
C
1.
The electric motor
A
2.
Harmonic gear
drives torque tube
3.
Torque tube
4.
Torsion bar
5.
Lever
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E
C
D
B
drives harmonic gear
drives torsion bar
moves lever
moves coupling rod
B
via a toothed belt
C
D
E
F
677_014
Harmonic drive gear
Design and function
Harmonic Drives are a strain wave gearing system used
wherever zero backlash, precision and high reliability are
required. They are ideal for the operation of the actuators
of the active suspension system. As the main component,
they transmit the rotation of the electric motor into relatively small angles of rotation and high torque to the
torque tube/torsion bar which are converted into the vertical motion of the coupling rod. Harmonic drives are used
extensively in robotic devices because of their precision (no
backlash), reliability and long service life. Harmonic drives
were first used by Audi in the dynamic steering system of
the Audi A4.
By inserting the wave generator into the flex sleeve, the
flex sleeve takes on the elliptical shape of the wave generator. When the wave generator rotates, it causes the flex
sleeve to radially deform. The external teeth of the flex
sleeve only mesh with the internal teeth of the circular ring
gear in two places around the circumference of the ring
gear as the wave generator rotates.
Harmonic drive component sets consist of only three components: wave generator, flex sleeve and circular ring gear.
The elliptical shaped wave generator is the driven element
of the gear set and has specially designed ball bearings.
The flex sleeve is a high strength torsionally stiff yet flexible shell-like component with external teeth which reliably
transmits high loads.
The outer circular ring gear has internal teeth. It is
installed over the flex sleeve. The rigid ring gear has two
teeth more than that of the flex spline.
Flex sleeve and wave generator
402_011
Ring gear with internal teeth
Wave generator with special ball bearings
Flex sleeve with external teeth
677_018
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When the electric motor is actuated, the wave generator
rotates. Because the number of teeth on the flex sleeve and
on the ring gear are not the same, the teeth on the flex
sleeve do not mesh exactly with the teeth on the ring gear.
The teeth on the flex sleeve engage the tooth flanks of the
ring gear in a laterally offset manner. This eliminates
backlash.
The force acting on this tooth flank produces a minimal
continuous rotational movement of the ring gear.
All the teeth on the circumference of the ring gear mesh in
a time-shifted manner due to the “rotation” of wave
generator.
Laterally offset meshing of flex sleeve and ring gear teeth
W = 0°
R = +0°
W = 90°
R = +0.88°
W = 180°
R = +1.76°
W = 270°
R = +2.65°
402_013
W = 360°
R = +3.53°
Wave generator = W
Ring gear = R
402_014
All the teeth on the circumference of the ring gear mesh in
a time-shifted manner due to the “rotation” of wave
generator. This produces a continuous rotational movement
of the ring gear at a defined ratio without any backlash.
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This illustration shows the difference in movement
(measured in degrees) between the wave generator and the
ring gear. The ratio can be changed during the design
process by changing the number of teeth.
Electric motor
Design and function
The drive source for the actuator is a star connected
permanently excited 48 Volt AC motor with five pole pairs
with electronic commutation (brushless). The maximum
power of the motor is approximately 2.0 kW; this is
however only briefly required within a few milliseconds. The
average power required is relatively low and is between
approximately 10 and 200 watts, depending on the driving
style and the road conditions.
The motor is activated by AC voltages between
0 and 48 Volts with a phase rotation of 120°. This
generates currents in the stator coils in alternating
directions (see illustration below). Corresponding magnetic
fields are generated around the coils through which the
current is flowing. Their polarity changes each time the
direction of the current changes. This generates a magnetic
field with rotating polarities which surrounds the rotor. This
magnetic field exerts corresponding force effects on the
permanent magnets which are permanently connected to
the rotor, thereby generating a torque which causes the
rotational movement of the rotor. Depending on the
activation (rotational direction of the magnetic field),
turning clockwise or counter-clockwise can be achieved.
The position of the rotor is detected by a sensor. This
sensor is on the end of the rotor, on the opposite end to the
belt pulley. There is a permanent magnet in the hollow
shaft of the rotor. Its position is measured by a
magnetoresistive sensor. The magnetoresistive measuring
principle is based on the fact that the electrical resistance
in ferromagnetic metals changes due to the effects of
external magnetic fields. Analyzing the changes in
resistance allows the position of the magnet in the rotor
shaft, and therefore also the angle of the rotor, to be
determined.
48V -DC voltage
(negative)
48V -DC voltage
(positive)
Sensor wire: rotor
position sensor control module
48V cable for Front
Suspension Stabilization
Actuator (AC voltage)
676_015
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In section 2, the greatest voltage is at V so the current
changes direction and flows from V to U. The rotating
magnetic fields generated by these alternating currents
cause corresponding force effects on the permanent
magnets of the rotor, which then generate torque.
The image shows the voltage curve of the phases. Electric
currents are generated by corresponding differences in
potential between the individual phases. The flow of
current through the coils is shown as an example in section
1 of the graph. As the phase voltage U is the greatest in
this section, the induced current flows from U to V and W
via the star point.
48V
U
Phase U
Phase V
Phase W
0
Current flow
1
2
90°
U
V, W
V
U, W
120°
W
180°
U, V
U
270°
V, W
V
U, W
360°
W
U, V
U
V
W
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676_017
Suspension stabilization control modules
The electric motors are activated on a per axle basis by
separate control modules. The control modules are
supplied 12V Terminal 30 power which enables their
participation in the vehicle Networking system and a 48V
power supply (Terminal 40) for the power path.
Both Suspension Stabilization Control Module 1 J1152 and
Suspension Stabilization Control Module 2 J1153 are
controlled by Drivetrain Control Module J775. They
communicate via a sub-bus system.
The control modules are installed between the actuators on
the subframes of the front and rear axles. They are flush
mounted with the surrounding components which provides
external protection.
Suspension Stabilization
Control Module 1 J1152
677_019
Front axle unit: the control module, actuators and integrated connector console with wiring.
Suspension Stabilization
Control Module 2 J1153
677_020
Rear axle unit: the control module, actuators and integrated connector console with wiring.
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Drivetrain Control Module J775
Drivetrain Control Module J775 (2nd generation) includes
the regulating software for the active suspension in addition to the regulating software for other suspension system
features and the corresponding sensors. It acts as the
master control module for the Suspension Stabilization
Control Modules. J775 communicates with the other data
bus nodes via FlexRay and with the Suspension Stabilization Control Modules via a sub-bus.
The regulating software is modular and mainly contains the
modules described below. A more detailed description of
the functions can be found on the following pages in the
“System functions” chapter.
Drivetrain Control Module J775
Body control module
The aim is to pacify the vehicle body and to neutralize road
excitation of up to approximately 5 Hz. Vehicle body vibrations have a frequency range of approximately 1-5 Hz.
Preview module
This module evaluates data from the front camera to detect
the surface of the road ahead. This enables the vehicle to
react to upcoming road excitation (for example, speed
bumps or bumpy road surfaces) in time, providing a significant increase in comfort.
Pitch module
The pitch of the vehicle (rotational movement about the
vehicle’s transverse axis) when moving off and braking is
reduced. This positively influences the vehicle’s dynamics
and comfort by shortening the braking distance and better
supporting the vehicle body.
677_021
Roll module
The roll of the vehicle (rotational movement about the
vehicle’s longitudinal axis) in corners is reduced. This positively influences mainly driving dynamics and driving safety
due to better steering response and neutral vehicle handling.
Crash module
If an impending side impact is detected, that side of the
vehicle is raised very quickly. Instead of impacting the door
area, the colliding object hits a larger proportion of the
more rigid sill area, which can reduce the effects of the
accident.
Elevated entry module
When a door is opened, the vehicle body is raised to make it
easier to get in/out of the vehicle.
677_022
J775 detects the rotational movement of the vehicle around the main axes and the vertical acceleration of the vehicle body.
Additional data is read in to determine the full current status of the driving dynamics (for example, the lateral acceleration
from the Airbag Control Module, the vehicle speed from the ABS Control Module.
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System functions
Basic function
The regulation of the stabilization rates, air springs and
dampers is closely linked. The air spring system assumes
the task of balancing the load and implementing both
manual and automatic changes to the specified vehicle
level. The damping required due to the actuators is taken
into account when the damping forces are calculated.
The basis for the calculation of the coupling force/tension
of the torsion bars required is both the Audi drive select
setting chosen by the driver and the relevant driving state
or the vehicle dynamics determined by the relevant
sensors. Corresponding sensors are implemented in J775
itself. Torques are measured about the x axis (roll torques),
the y axis (pitch torques) and the z axis (yaw torques). The
yaw torques are used to estimate the lateral acceleration;
these figures are then compared with the measured values
from the Airbag Control Module. Special software determines the vehicle speed. The vehicle level is determined, as
with adaptive air suspension (AAS), by four separate level
senders. The vertical movements of the vehicle body are
measured by an acceleration sensor, which is also part of
the running gear control unit.
Drivetrain Control Module J775 calculates the torque with
which the torsion bar should be tensioned for each wheel
individually and almost in real time. This torque corresponds to a defined angle of rotation at the output of the
harmonic drive gear.
These angle figures are provided as control inputs to Suspension Stabilization Control Modules 1 and 2 for the front
and rear axles. The control modules achieve these positions
by activating the electric motors of the actuators. The
measured values from the rotor position sensors form the
basis for determining the angles.
The total ratio for the angle of rotor rotation to the angle
of rotation at the drive gear output is 189:1 (belt drive of
rotor – drive gear input: 1:2.36: drive gear input – drive
gear output: 80:1). This means that the rotor of the electric
motor must turn 189 times to achieve one rotation at the
drive gear output.
Driver Assistance Systems
Control Module J1121
The actuators are always supplied with current during
active operation. There are phases of electrodynamic
damping in every control operation. The permanently
excited rotors of the electric motors are then “driven”. The
rotating magnetic fields generated as a result induce electric voltages in the stator coils. The electric currents generated are used for recuperation of the 48 Volt battery. The
maximum recuperation is approximately 3 kW; this may
however only be effective very briefly.
Drivetrain Control Module
J775
Actuators on
front axle
Active suspension - software
Sensors for
vehicle dynamics
Front camera
Preview module
Activation
of actuators
Measured values
from rotor position
sender
Suspension
Stabilization
Control Module 1
J1152
Additional external
messages/signals
Vehicle level sender
Angle at output of
harmonic drive gear
Body control module
Vehicle level sender
Pitch module
Audi drive select
module
Vehicle level sender
Roll module
Suspension
Stabilization
Control Module 2
J1153
Activation
of actuators
Actuators on
rear axle
Vehicle level sender
Measured values
from rotor position
sender
Additional internal
signals
Audi drive select
setting
677_023
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The system principle is illustrated using the example of
driving over a bump (“positive” obstacle) with the left front
wheel. The aim of the regulating activities is to calm the
vehicle body as far as necessary to achieve the best possible
compromise between driving comfort and dynamics.
Dynamics and comfort are weighted on the basis of the
Audi drive select setting chosen by the driver.
› When the bump is reached, the vehicle body experiences
vertical acceleration (z direction) at the front axle/above
the left front wheel. This vertical acceleration is measured by the sensors in Drivetrain Control Module J775.
In addition, the suspension at the left front wheel may
compress slightly. This is also detected by the allocated
vehicle level sender. Alongside a large amount of additional information (for example, vehicle speed, lateral
acceleration etc.), this information is evaluated by J775.
J775 proceeds to reduce the damping force of the left
front damper in the compression stage. At the same
time, the control module determines how much the
tension of the torsion bars of the actuators on the front
axle (stabilization rate) needs to be reduced by to calm
the vehicle body accordingly. The control module calculates the changes to the angles of rotation of the actuators required to do so and requests that this be implemented by chassis Suspension Stabilization Control
Module 1 J1152 on the front axle.
677_022
› The lower damping force and stabilization rate allows
for suitably large spring deflection on the front wheel.
The vertical forces applied to the vehicle body are
thereby reduced. The acceleration of the vehicle body
is restricted to a level which is comfortable for the
occupants.
› When the rear axle reaches the bump, the dampers
and actuators on the rear axle go through the same
processes as those specified above.
Right Front Level
Control System Sensor
G289
Suspension Stabilization
Control Module 1 J1152
Drivetrain Control Module
J775
Actuator
Left Front Level
Control System Sensor
G78
677_024
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Additional preview function
Additional functions
In addition to the basic functions, additional functions can
be achieved by the active suspension.
One function makes use of the option to detect certain
irregularities in the road surface in advance. This is achieved
by evaluating the optical signals from Driver Assistance
Systems Front Camera R242. Driver Assistance Systems
Control Module J1121 evaluates the camera data according
to defined criteria. It determines the height and, on that
basis, the type of obstacle. Typical obstacle types include
harmonic bumps and speed bumps. Smaller road
irregularities (potholes) are usually not detected due to
their “edges” being on the same level as the road itself.
Drivetrain Control Module J775 also receives information
about the resolution quality from Driver Assistance
Systems Control Module J1121 to assist it with the
analysis.
On the basis of this information, J775 decides on the
relevance of regulating and the ongoing procedure. Driver
Assistance Systems Control Module J1121 provides
Drivetrain Control Module J775 with current data
approximately 18 times per second.
The main benefit of the preview function is the option of
initiating corresponding measures in advance. The basic
function can only be activated when measured values
from the relevant sensors show that the vehicle has
already begun driving over the obstacle. With the preview
function, the counter-measures have already been
initiated when the front wheels reach the obstacle. The
function is active at speeds of up to approximately 37.28
mph (60 km/h). The preview function has the following
regulating components:
677_025
Pro lift
Pro comp
When the vehicle drives over a “positive” obstacle (for
example, speed bump, see image), the vehicle’s suspension
compresses. Vehicle occupants find it particularly uncomfortable if the entire spring travel is used during spring
deflection. If the preview function detects a “positive”
obstacle, pro lift initiates a corresponding activation of the
actuators. The vehicle body is raised early so that there is
sufficient spring travel available when the vehicle drives
over the obstacle. As a result, it is possible for the vehicle
to be raised by up to 1.57 in (40 mm) before it reaches the
obstacle, depending on the type of obstacle detected. This
occurs gently and is hardly noticeable for the driver.
Almost exactly at the same time that the relevant wheel
“arrives” at the obstacle, this regulating component initiates a further regulation to follow the contour of the obstacle. This actively moves the wheel towards the vehicle body
by activating the relevant actuator. This corresponds to a
spring travel movement. Thanks to pro lift, it has already
been ensured that sufficient spring travel reserves are available. The aim is to eliminate (or at least significantly
reduce) the impulse caused by the ramp-shaped contour of
the obstacle at the moment when it first makes contact
with the wheel. As part of this, the damping forces are also
adjusted accordingly. A similar process occurs when the
vehicle is moving off the obstacle. In this case, the wheel’s
suspension is actively extended so that it can follow the
contour of the road closely as possible.
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677_026
An obstacle is detected by evaluating the camera data. It is classified as a “positive” obstacle (protruding from the road
surface). For this type of obstacle, the highest level of spring travel possible must be made available. Drivetrain Control
Module J775 calculates the specified angle for the lever and requests that Suspension Stabilization Control Modules 1 and 2
implement this. The vehicle body is raised accordingly before the wheel reaches the obstacle. The spring travel available is
thereby increased by up to 1.57 in (40 mm).
677_027
Immediately before the calculated moment that the vehicle arrives at the obstacle, Drivetrain Control Module J775 triggers
the process to raise the wheel affected. This avoids hard contact with the obstacle.
677_028
“Leaving” the obstacle is supported by adjusting the vertical movement of the wheel to the contour of the obstacle. The
extension of the springs is supported, if necessary, by the active activation of the actuator.
24
Additional crash lifting function
Despite many protective systems, injury to the occupants cannot be ruled out in the event of a traffic accident. Side collisions
also constitute a certain injury risk for the vehicle occupants affected. The main cause of this is the relatively small space for
deformation between the vehicle occupants on the side of the collision and the exterior of the vehicle. The structural elements
in-between must absorb the kinetic energy of the colliding vehicle.
Depending on the force of the impact, the structural elements may deform in the direction of the vehicle interior (intrusion).
Side collision without crash lifting function
677_029
Side collision with crash lifting function
677_030
The area surrounding the side of the vehicle is monitored by four corner radar sensors, which are also required for Audi pre
sense side. Driver Assistance Systems Control Module J1121 evaluates these data.
Depending on the situation, it determines the potential risk posed by a vehicle approaching from the side. It calculates the
criticality (a numerical figure which represents the potential risk from the approaching vehicle) and the expected time until
the collision. This information is sent to the Airbag Control Module J234 which initiates the following actions if necessary
(pre sense side cascade). As part of this, Drivetrain Control Module J775 is requested to raise the vehicle for a collision.
If the relevant object/vehicle is no longer in the detection area, the request is canceled by the Airbag Control Module and
the vehicle is returned to its original level.
If the less common case occurs in which a vehicle on a collision course swerves away, the vehicle is lowered again after a
defined period of time. The collision function is also active in towing mode, with unchanged parameters.
For the collision function to be activated when necessary, all doors, the trunk and hood lids must be closed, Terminal 15
must be activated and the vehicle must have exceeded a speed of 4.9 mph (8 km/h) once. The function is no longer active
when a door is opened or Terminal 15 is switched off. The collision function is also deactivated if ESC and/or pre sense is
deactivated.
25
Additional elevated entry function
This optional function raises the vehicle body when a door is opened. The vehicle is raised approximately 1.57 in (40 mm)
(compared to the reference level in Audi drive select mode “auto” or “comfort”) in approximately one second.
The original level is reset:
› Approximately 10 seconds after all four doors have been closed.
› When the vehicle starts moving.
› When the vehicle is locked.
› When the Audi drive select mode is changed.
› When the engine is switched off and the door is open, after a defined period to retain the battery charge level.
The raised condition is displayed in the MMI touch screen.
677_032
Additional corner tilting function
This function is only activated if the comfort+ mode is chosen in Audi drive select.
Because of the centrifugal forces acting on the vehicle body in corners, the body tilts towards the outside in corners. This
undesired (from the perspective of driving dynamics and comfort) roll is reduced by the active damping control or largely
neutralized if the vehicle is equipped with electromechanical roll stabilization.
The active suspension regulates in a more engaged manner in corners because it actually tends to tilt the vehicle body in the
opposite direction. This is done by lowering the body on the inside of the corner and raising it on the outside. This causes the
vehicle to tilt up to approximately 3° into the corner and achieves even more effective support via the wheels on the outside of
the corner. At the same time, a significant improvement in comfort for the vehicle occupants is achieved as the lateral forces
acting on them are reduced.
The regulating software mainly evaluates the vehicle speed and the lateral acceleration transmitted by the Airbag Control
Module.
Key
Vehicle body tilt in corners
caused by the centrifugal force
acting on the vehicle’s center of
gravity
Vehicle body tilt in corners
caused by the active suspension
26
677_033
Additional helicopter function
Forces also act on the vehicle body when undergoing
longitudinal acceleration (forward propulsion or braking).
When the vehicle accelerates, the body supports itself on the
wheels of the rear axle due to the effect of the inertial force;
the load on the front axle is reduced. As a result, the rear axle
suspension deflects and the front axle suspension extends.
When the vehicle is braking, the inertial force works in the
opposite direction; the suspension deflects at the front axle
and extends at the rear axle. On vehicles with damping
control, these pitching movements are counteracted by
adjusting the damping forces.
The regulating function of the active suspension also works
to compensate for the effects of these dynamic driving
situations. Under braking, the front axle is not only prevented from dipping forward, but the body is actually raised
slightly at the front.
When the vehicle accelerates, the system regulates in the
opposite direction and causes the body to be lowered (suspension compressed) at the front axle and the suspension to
be extended at the rear axle.
This raising/lowering is mostly unnoticeable for the vehicle
occupants. What can be noticed, however, is increased
seating comfort thanks to the reduction of longitudinal
forces acting on the occupants in or against the direction of
travel.
677_035
Raising the vehicle at the front axle and lowering it at the rear axle under braking counteracts the inertial force and enables
significant comfort improvements by reducing the longitudinal forces acting on the occupants.
677_034
When the vehicle is accelerating, the body is lowered at the front axle and raised at the rear axle. A significant improvement in
comfort due to a reduction in the longitudinal forces acting on the occupants is also the result here.
27
Operation and servicing
Operation and driver information
The driver cannot deactivate the basic functions of the active
suspension, but can directly influence the regulation through
Audi drive select. The driver also has the option of being
informed of the status of the function while the system is
actively regulating. To do this, the menu option “Active
suspension” must be selected (Car – Vehicle info – Active
suspension). The display shows, for each wheel individually,
to what extent the movements of the vehicle body are being
compensated for. The driver can also choose to what extent
the system should compensate for bumps in the road.
Audi drive
select
Active
Suspension
Efficiency
assist
A/C
Lights & vision
Parking aid
By selecting the sprocket symbol in the active suspension
display, the driver can switch off the unevenness compensation function (preview function) or choose between gentle
and strong unevenness compensation.
The elevated entry function can also be activated or deactivated by the driver. Detailed information on the operation
and displays of the relevant vehicle model can be found in
the Owner’s Manual.
Seats
Driver assist
systems
Car Active suspension
Car Active suspension
Analysis of road ahead: unevenness compensation
Off
Low
High
Elevated entry
677_037
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System behavior in the event of a fault
Drivetrain Control Module J775 performs a system diagnosis
and reacts accordingly to implausibilities, system faults and
special effects in the immediate surroundings (temperature,
system utilization and electrical load).
The driver may be notified via warning lamps (neutral white,
yellow, red) and a driver message. The warning lamp symbol
is identical to the symbol for the air suspension system. The
driver message indicates whether the notification is about
the air suspension or the active suspension. The various
displays are described in the Owner’s Manual.
677_039
A two-level concept of system degradation has been developed. The aim is to avoid emergency running mode. The first
level involves a relatively small reduction in the power and
torque of the actuators. The negative effects caused to
comfort are, for the most part, not noticeable to the vehicle
occupants. The driver is informed of the activation of the
second level by a white warning lamp and a text in the
display. The reduction in the vehicle’s roll rigidity achieved in
this level approximately corresponds to that of the normal
running gear.
677_040
If an actuator fault is detected, all actuators are switched off
and the dampers are actuated with constant current. This
achieves significant hydraulic damping which allows for
sufficient roll stability with corresponding restrictions in
comfort. The driver is informed of emergency running mode
by the yellow warning lamp and a corresponding text.
677_039
If there is a fault on a damper, the activation of the damping
valves of all dampers is switched off. A damper fault has no
effect on the activation of the actuators. Here, the driver also
receives a fault message via the activation of the yellow
warning lamp and a text on the display.
677_042
677_039
29
If a vehicle level sender fails, the damping valves also receive
constant current and the activation of the actuators is
switched off. As a result, significant damping forces are
achieved on the front and rear axles. The driver is also
informed of this via the yellow warning lamp and a corresponding text.
677_041
677_039
If there is a fault with Drivetrain Control Module J775 which
makes it necessary to switch off the actuators, the air spring
system and the damping control are also affected because
this module is also responsible for regulating these systems.
This condition is shown by the red warning lamp. Because it
is only possible to continue driving the car with restrictions
due to significantly reduced stability, a driver message is
displayed requesting the driver to stop the vehicle.
677_038
677_039
30
Service operations
The following components can be replaced if necessary:
› The entire module, including the control module,
actuators and integrated connector console.
› The wiring harnesses.
› The stone deflector covers for the control motors on the
rear axle.
The Suspension Stabilization Control Modules have the
following Address Words:
› 00D4 - Suspension Stabilization Control Module 1
J1152.
› 00D5 - Suspension Stabilization Control Module 2
J1153.
Basic setting is required for each of these modules after
they have been replaced. This involves allocating the vehicle
ride heights (measured values from vehicle level senders)
at the four wheel positions to the relevant actuator angles
(measured values from the rotor position senders) and
storing this information in the control modules.
The vehicle ride heights were already adapted when Basic
setting of Drivetrain Control Module J775 was performed.
This involved allocating the measured values from the
vehicle level senders to the actual ride heights measured at
the four wheel positions.
Therefore, after successfully performing Basic setting of
control modules J1152 and J1153, intended changes to the
vehicle ride height can be converted directly into the angle
changes required at the actuators/electric motors by the
control modules and also set accordingly.
677_043
The crash lifting function must be deactivated for work in
an inspection pit or on a hoist. This is done by switching off
the ignition (Terminal 15 off) and opening the driver’s door
once. On vehicles with active suspension, the vehicle may
raise or lower itself via the elevated entry function when
the ignition is switched off. This function must also be
deactivated. For information on this, please refer to the
Owner’s Manual.
The active suspension actuators operate at 48V. It is
required that the system be de-energized before performing relevant removal/installation procedures. Follow all
work steps and sequences specified in ElsaPro.
System behavior in Shipping Mode
Regulation remains active in Shipping Mode. However, the
elevated entry function is deactivated. This prevents the
vehicle’s ride height from being raised when a door is
unlocked/opened. This reduces the possibility of damage to
body panels when vehicles are loaded and unloaded from a
car transporter.
System behavior in Transport Mode
Regulation is deactivated in Transport Mode. This relieves
the load on the electrical system because the battery is not
utilized by the regulating processes.
Note
Caution! Before working on vehicles with active suspension, read and follow all the safety precautions given in
ElsaPro.
31
Knowledge assessment
An On-Line Knowledge Assessment (exam) is Available for this eSelf-Study Program.
The Knowledge Assessment is required for Certification credit.
You can find this Knowledge Assessment at: www.accessaudi.com
From the accessaudi.com Homepage:
› Click on the “App Links”
› Click on the “Academy site CRC”
Click on the Course Catalog Search and select 960393B - “Active suspension”.
Please submit any questions or inquiries via the Academy CRC Online Support Form
which is located under the “Support” tab or the “Contact Us” tab of the Academy CRC.
Thank you for reading this eSelf-Study Program and taking the assessment.
32
960393
All rights reserved.
Technical specifications subject to
change without notice.
Audi of America, LLC
2200 Ferdinand Porsche Drive
Herndon, VA 20171