Get Running gear -> Adaptive air suspension Guide for Audi RS E Tron Gt 4 Door First Generation (2021-2026)

Adaptive air suspension

Overview

Adaptive air suspension with electronic damping control is standard equipment on the Audi RS e-tron GT and optional equipment

on the Audi e-tron GT. The system’s construction fundamentally corresponds to the adaptive air suspension systems used on other

Audi models, in particular the Audi Q7 (type 4M). However, the system components partially vary and are presented in detail below.

Air springs with three separate air chambers are being used in an Audi model for the first time.

This allows different air spring volumes to be achieved using integrated electrically switchable valves. Another new feature is that

the acceleration of unsprung masses can be detected by four separate sensors. The running gear control unit J775 remains the con-

trol centre for the air suspension and damping on the Audi e‑tron GT.

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System components

Running gear control unit J775

Overview

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As with other Audi models on the MLB platform, the running gear control unit is also the central regulating unit for various running

gear systems on the Audi e‑tron GT. The tasks of the control unit include damping control and regulation of the vehicle level (adap-

tive air suspension). The basis of this is an analysis of the current dynamic driving state (evaluation of longitudinal, lateral and ver-

tical acceleration along with the yaw, roll and pitch rate) in real time. These data (from external sensors (refer to image

“684_342”)) are the basis for determining the driving state. The control unit communicates via FlexRay channel A, which is fitted in

the luggage compartment (left-side).

Data transfer

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Service operations

The following new features regarding the air suspension are present in the service functions of control unit J775 in the Audi e-

tron GT:

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A new function “0074 - Replacement work on air suspension system” has been introduced to replace air springs. In the sub-menu,

the user can select whether just one air spring is to be replaced or whether the entire system is to be bled/filled up. As previously,

the vehicle must be on a lifting platform with its wheels off the ground before work is started. This prevents damage to the air

springs which are bled. Regulation by the program is deactivated at the beginning of the bleeding process. The system is bled on

the basis of an accompanying pressure measurement up to a maximum remaining air spring pressure of approx. 4 bar. Only then

can the air system be opened safely to remove the air spring affected.

The system is filled using the accumulator. A minimum air pressure of 12 bar is required to do this. If the measured accumulator

pressure is lower, the accumulator is initially filled to a pressure of >12 bar. The system is then filled a maximum of 10 times. If

the minimum pressure cannot be reached, the mechanic is informed that there is a system fault (e.g. a leak). The air spring(s) are

also filled on the basis of an accompanying pressure measurement. An air pressure of between approx. 4 bar and a maximum of

7.2 bar will be set. The height regulation will be reactivated after the system has been filled successfully.

Note

It is very important that you observe the information in the Workshop Manual related to handling the air springs. In-

correct handling may cause damage or premature failure.

If the “Venting / filling entire suspension system” function is performed, the air dryer is regenerated after the system has been

filled. This involves fully bleeding the accumulator and then filling it back up to a pressure of approx. 18.5 bar. In the bleeding

process, dry air flows through the dryer and transports the moisture bound in the drying granulate out of the system into the at-

mosphere.

Additional diagnosis functions correspond to those in other Audi models. After removal/installation of certain components (e.g.

control unit J775, vehicle level senders), the vehicle height level must be re-adapted on vehicles with adaptive air suspension or

electronic damping control.

System faults are indicated to the driver via the activation of the familiar air spring symbol in conjunction with an explanatory text.

The relevant messages are described in the Owner's Manual. Depending on the fault category, the symbol is either red or yellow, as

on previous vehicles.

Air spring strut, front axle

The air springs on the front axle consist of three differently-sized chambers which are connected together. Two electrically switcha-

ble valves can be used to separate chambers. One valve separates volume 1 from volume 2, the other separates volume 1 from

volume 3. There is no direct link between volume 2 and volume 3. As a result, it is possible to achieve three different air volumes.

The larger the air volume achieved is, the smaller the spring rate will be. This makes spring extensions and compressions corre-

spondingly more comfortable. Smaller air volumes with larger spring rates are more suitable at high speeds or for dynamic driving.

Because the air volume can be changed quickly depending on the situation, it is particularly easy to regulate the suspension to react

to different driving conditions.

Air spring volumes:

Volume

Feature

Volume 1 + volume 2 + volume 3

Volume 1 + volume 2

Volume 1 + volume 3

Volume 1

Highest volume, lowest spring rate, most comfortable setting

Medium volume

Small volume, high spring rate, dynamic setting

Smallest volume, highest spring rate, most dynamic setting

At vehicle speeds of < approx. 220 km/h and little or no longitudinal or lateral influences, all three air volumes are usually activa-

ted. At high speeds or in the event of increasing dynamic influences (lots of corners, braking and acceleration), volumes 2 or 3 may

be switched off as necessary.

The switching valves are directly activated by running gear control unit J775 via two discrete wires. In their neutral, non-activated

status, both valves are open (low spring rate - “soft” suspension). This status is present after the vehicle has been parked and as

part of certain faults which lead to regulation being deactivated.

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Air spring on rear axle

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Springs and dampers are fitted in a separate layout on the rear axle as individual components. The air springs on the rear axle also

consist of three chambers which are connected together. Two electrically operated valves can be used to separate chambers. The

system works in the same way as the air spring system on the front axle.

Air supply unit

The compressor generates the relative system pressure of approx. 18 bar (maximum pressure approx. 25 bar). It compresses the

air drawn in via the intake silencer and the filter in a two-stage compression process. The electric compressor works with two pis-

tons. Its design and functions correspond to the component in the Audi Q7 (type 4M).

Reference

For further information, please refer to (refer to chapter “Chassis with air suspension and electronic damper control

(adaptive air suspension)”) in SSP 633 “Audi Q7 (type 4M) Chassis.”

The air supply unit is also fitted at the rear of the vehicle in the Audi e-tron GT. Rubber bushes ensure effective acoustic decoupling

and reduce the amount of structure-borne sound in in the body structure. Additional components of the air supply unit are the air

dryer and a solenoid valve for the boost function. The module also includes a pneumatically operated exhaust valve and a solenoid

valve to actuate it. The design and construction again correspond to that of the of the compressor module in the Audi Q7 (type 4M)

and the description in SSP 633.

A pressure relief valve is fitted in the compressor module of the Audi e‑tron GT. When air is released or pressure is dissipated in the

system, this ensures that the system pressure does not drop below 2 bar. The residual pressure valves fitted directly on the air

connections of the air spring struts on some other Audi models are also fitted on the Audi e‑tron GT. This ensures that a small air

pressure of approx. 1.5 bar remains in the air springs even in the event of a loss of pressure due to leakages in the lines.

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The electric motor is activated by a separate control unit which is fitted on the same bracket. As on the Audi Q7 (type 4M), activa-

tion is via a PWM signal. This makes it possible to start the motor “gently” without significant current peaks. A compressor-temper-

ature model has also been implemented on this control unit. It monitors the compressor temperature on the basis of the outside

temperature, vehicle speed and compressor running time. If defined temperature values are exceeded as part of this, regulating

processes upwards (raising the vehicle by actively running the compressor) are restricted or disabled until the temperature falls

accordingly. At this time, no mode changes can be made in Audi drive select which would require the vehicle to be raised.

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Solenoid valve block

The solenoid valve block has the same design and functional principle as in the Audi Q7 (type 4M).

Reference

For further information, please refer to (refer to chapter “Chassis with air suspension and electronic damper control

(adaptive air suspension)”) in SSP 633 “Audi Q7 (type 4M) Chassis.”

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Accumulator

The cylinder-shaped accumulator is made of aluminum and has a capacity of 8 litres. It is fitted in the rear of the vehicle. Regulat-

ing processes are performed using the pressure in the accumulator as a priority. This is done to limit the running time of the com-

pressor and to improve the interior acoustics. This requires sufficient pressure in the accumulator. The accumulator is filled up

while the vehicle is moving. The vehicle can be raised from the low level to the normal level approx. four times with the accumula-

tor filled up (to a system pressure of approx. 18 bar). The control unit determines the pressures in the air springs and the accumu-

lator by activating the correspondingly allocated solenoid valves and taking measurements via the pressure sensor integrated in

the solenoid valve block. These measured values form the basis for calculating the pressure differences between the accumulator

and the corresponding air spring. There must be a pressure difference of approx. 2 bar between the accumulator pressure and the

air spring pressure to increase the air volume in an air spring with the help of the accumulator. The accumulator also “provides” the

energy for the boost function, thereby ensuring that pressure can be built up quickly.

Reference

For further information on the pressure measurement and boost function, please refer to SSP 633 "Audi Q7 (type 4M)

Chassis".

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Vehicle level senders

The four vehicle level senders are Hall senders and provide the processed measured values to the running gear control unit in the

form of PWM signals. The four senders on the front and rear axles are identical. The brackets and linkages have been geometrically

adapted to the different connection points on the front and rear axle.

The service operations for removal and installation or replacement correspond to those for the vehicle level senders already in use

in other Audi models. Calibration is required after a sender is replaced: 0074 – Basic setting – Calibration of height sensors.

Any sensors/systems affected must subsequently be re-adapted/calibrated.

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Note

Please note the instructions in the Workshop Manual.

Vehicle level senders on front axle

Position of vehicle level sender on front axle – lever/linkage

connected to upper wishbone

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Vehicle level senders on rear axle

Position of vehicle level sender on rear axle – lever/linkage

connected to lower wishbone

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Wheel acceleration senders

The four wheel acceleration senders are being used on an Audi model for the first time. They detect the accelerations of the

wheels/the unsprung masses in the vehicle’s vertical (z) and lateral (y) directions. The measurement is made using the seismic

mass principle.

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Reference

Further information on how this measurement works can be found in SSP 458 "Audi A8 10 Running gear and suspen-

sion" in the section “Control unit for sensor electronics J849”.

The senders are fitted on the hub carriers of the front and rear axles.

The technical basis is the PSI5 sensor bus system (Peripheral Sensor Interface 5). This standardised system is very effective and has

low data transfer rates of <200 kbit/s. The sender is directly connected to the running gear control unit via a two-wire bus. The

sensor uses this bus both for data transfer and for its power supply from the running gear control unit. The running gear control

unit controls the communication via synchronisation impulses which are answered by the sender with corresponding data pack-

ages. The running gear control unit converts the signals received at a frequency of 120 Hz into digital square-wave signals and de-

codes the data received.

No further activities (calibration etc.) are required after a wheel acceleration sender is replaced in service.

It is possible to check whether the sender is fundamentally working properly by tipping it 180° out of its normal installation posi-

tion. If the sender is working correctly and the wiring is intact, negative actual values will be displayed as measured values.

Position of wheel acceleration sender on front axle

Position of wheel acceleration sender on rear axle

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Body acceleration senders

The four senders measure the acceleration of the vehicle body. This means the sprung masses in z direction and the longitudinal

accelerations in x direction. In the area of the front axle, the senders are fitted on the suspension turrets and at the rear they are

fitted on the side of the body behind the rear axle. Their design and functional principle largely corresponds to that of the wheel

acceleration senders. They are also connected to the running gear control unit via a PSI5 two-wire bus. In this case, the signal is

transmitted at 60 Hz; the measurement range is approx. +/- 1.6 g.

No further activities (calibration etc.) are required after a body acceleration sender is replaced in service.

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As with the wheel acceleration senders, it is possible to check whether the sender is fundamentally working properly by tipping it

180° out of its normal installation position. If the sender is working correctly and the wiring is intact, negative actual values will be

displayed as measured values.

Position of body acceleration sender in area of front axle

Position of body acceleration sender in area of rear axle

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Air lines, line connections, line connectors

The air lines which connect the air supply unit (solenoid valve block) to the air springs are fitted in the electrical wiring harness. The

air line to the accumulator is a moulding. Repairs to the air line system are also defined for the Audi e-tron GT. They largely corre-

spond to those undertaken for other Audi models.

Note

Please note the information in the Workshop Manual.

How the system works

The general function of the entire system (generating and dissipating pressure, boost function, integration of accumulator in regu-

lating processes, actuation of solenoid valves, pressure measurements) corresponds to that of the adaptive air suspension in the

Audi Q7 (type 4M).

Reference

For further information, please refer to (refer to chapter “Chassis with air suspension and electronic damper control

(adaptive air suspension)”) in SSP 633 “Audi Q7 (type 4M) Chassis.”

The main new feature is the introduction of the three-chamber air springs. Their functions and the resulting benefits are described

in the “System components” chapter. Integrating the wheel acceleration sensors in the entire system for the first time increases

precision when detecting the vehicle dynamics. The development aim was to retain the familiar operating and display concept from

other Audi models with adaptive air suspension. The desired mode can also be selected in Audi drive select on the Audi e‑tron GT.

The modes have been specially defined and applied to the Audi e‑tron GT.

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Running gear -> Adaptive air suspension for Your Audi RS E Tron Gt 4 Door First Generation (2021-2026)

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