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AIRmatic suspension, function - GF32.22-P-4011SX

MODEL 221 with CODE (489) Airmatic (semi-active air suspension) up to Model Year 08/modification year 07 

Level control, function description 

Level control is realized by means of four suspension struts with integral bellows. If the AIRmatic compressor unit (A9/1) or AIRmatic central reservoir delivers air to a bellows, the vehicle level is raised at the associated wheel. Vice versa the vehicle level reduces if the air is drained out of the bellows via the corresponding level valve (integrated in the level control valve unit (Y36/6)) and the AIRmatic pressure reduction valve (A9/1y1) (integrated in the AIRmatic compressor unit) is drained.

The system is equipped with a central reservoir as a compressed-air reservoir. This reservoir increases the adjustment speed at which the vehicle level is raised and permits control even if the ignition is switched off.

By pressing the level adjustment switch (S6/2s10) in the cockpit switch group (S6/2), the driver can choose between normal level (NN) and a raised level (EN1), whereby the currently inactive mode is activated each time the button is pressed.

IMPORTANT The following values for the levels and the transient conditions may differ from variant to variant.

Levels: 

Transition conditions: 

The switch operations of the level adjustment switch with function LED (integrated in the cockpit switch group) are read in by the upper control panel control unit (N72/1) via the upper control panel LIN [local interconnect network]. The driver can choose between normal level (NN) and higher level (EN1).

The level adjustment switch has two switch positions:

The operation of the level adjustment switch is read in by the upper control panel control unit via the upper control panel LIN and is supplied to the AIRmatic with ADS control unit (N51) via the interior CAN, central gateway control unit (N93) and via the chassis CAN. Actuation of the function LED in the switch is reciprocal.

Lock position  (when working on vehicle and during diagnosis)

So that when the vehicle is raised intentionally, e.g. with a jack, air is not continuously drained out of the suspension struts in order to lower the vehicle, it is necessary to automatically detect this unloading of the wheels and from it to derive a blocking position.

The lock position is purely a software function which prevents actuation of the level valves (drain process). If the blocking position is detected by the AIRmatic with ADS control unit, there is no display in the instrument cluster (A1) and there is no fault storage.

The lock position is canceled automatically by the AIRmatic with ADS control unit provided that the condition "left/right front wheel speed > 0 km/h" exists. The level position functions are then reactivated. Actuation of the output stages by the AIRmatic with ADS control unit via the diagnosis function is performed irrespective of the lock position status, i.e. actuation is always possible.

Shock absorber adjustment, function description 

The control response of the AIRmatic with ADS control unit can be influenced by the driver using the transmission modes button (A40/9s8).

Actuation of the transmission modes button is read in by the front central operating unit (A40/9) and placed on the telematics CAN. The instrument cluster receives the signal via the COMAND controller unit (A40/3) and places it on the central CAN to the central gateway control unit.

The selection C  omfort-, S  port program and M  anual, (not with (code 494) USA version), is stored in the instrument cluster so that after an engine start the same performance map is valid as before switching off the ignition. The AIRmatic with ADS control unit receives the signal "S", "C" or "M" (not with code (494) USA version) from the central gateway control unit via the chassis CAN.

The function algorithm of the AIRmatic with ADS control unit distinguishes between two damper modes:

One of two damper modes is selected depending on the calculated vehicle excitation. The Comfort mode is selected individually for each wheel (if the degree of vehicle excitation permits this). For this purpose, both damping valves on a shock-absorber strut are constantly energized resulting in the softest shock absorber setting for the wheel in question. If the vehicle excitation exceeds a certain level, skyhook damping is activated for the wheel. If the vehicle excitation has diminished, the Comfort mode is reactivated.

When the vehicle is stationary, damping at all four wheels is set to soft. If the vehicle exceeds a defined minimum speed, the system switches to skyhook mode.

IMPORTANT The initial phase of a braking or acceleration operation also causes the shock absorber mode to shift toward "hard" in order to prevent the vehicle from pitching. If system components (e.g. valves or sensors) fail, the system automatically switches back to the fallback level "hard" (de-energized valves).

Display of fault and system messages 

The instrument cluster has a multifunction display (A1p13) for displaying system and fault messages together with advice for the driver.

To output messages the AIRmatic with ADS control unit transmits corresponding messages to the central gateway control unit via the chassis CAN and on to the instrument cluster via the central CAN. There are various fault messages and system messages with different fault priorities.

If several faults exist at the same time, several fault messages will be output accordingly.

Texts displayed in instrument cluster:

The following system message is also displayed in the instrument cluster:

Block diagram for air suspension with adaptive damping system (ADS) 

  Pressure supply, function   GF32.22-P-4010SX 
  Central reservoir component description   GF32.22-P-5102SX 
  Compressor unit, component description   GF32.22-P-5103SX 
  Pressure sensor, component description   GF32.22-P-5104SX 
  AIRmatic with ADS control unit, component description   GF32.22-P-5108SX 
  Suspension strut component description   GF32.25-P-5101SX 
  Level sensor, component description   GF32.31-P-5105SX 
  Acceleration sensor, component description   GF32.31-P-5106SX 
  Level adjustment switch, component description   GF32.31-P-5109SX 
  Comfort and sport switch, component description with code (494) USA version GF32.31-P-5110SXU 
  Damper valve, component description   GF32.31-P-5112SX 
  AIRmatic relay, component description   GF32.31-P-5114SX 
  Level control valve unit, component description   GF32.31-P-5115SX 
  Comfort/sport/manual switch, component description except CODE (494) USA version GF32.31-P-5116SX 
  Steering angle sensor, component description   GF42.45-P-5107SX
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