GF32.22-P-0003LEA AIRmatic, Function

GF32.22-P-0003LEA AIRmatic, function
- except CODE (487) Active Body Control (ABC)
- except CODE (Z07) Top protection
- with CODE (489) AIRMATIC (air suspension with continuous damper adjustment) in model 216
- as of model year 2010

Function requirements, general
^ No overvoltage or undervoltage
^ Circuit 30

AIRMATIC system, general
The AIRMATIC system is the combination of an air suspension with an automatic damper adjustment.

The aim is to keep the vehicle level constant. Automatic damper adjustment allows the suspension to be adjusted to the prevailing driving situation. The direction of movement of the vehicle body is used to determine the suitable level of damping force.

The last selected level as well as the last adjusted damping force stage is active after switching on the ignition.

The AIRmatic system consists of the following subfunctions:
^ System start-up function sequence
^ Compressed air supply function sequence
^ Level control function sequence
^ Lock position function sequence
^ Damper adjustment and chassis adjustment function sequence
^ System and warning messages function sequence

System start-up function sequence
The system is started when bus idle is canceled. This ensues by unlocking the central locking (CL) or by opening a vehicle door, the trunk lid being rated as a vehicle door.

The following signals are provided to the AIRMATIC with ADS control unit (N51) on the chassis CAN (CAN E):
- Status of central locking from EIS [EZS] control unit (N73)
- Status of front doors, from left front door control unit (N69/1) (model 221) or from left door control unit (model 216) and from right front door control unit (N69/2) (model 221) or from right door control unit (model 216) via interior CAN (CAN B)
- Status of rear doors (model series 221 only) from left rear door control unit (N69/3) and from right rear door control unit (N69/4) via the interior CAN
- Status of trunk lid from rear SAM control unit with fuse and relay module (N10/2) via the interior CAN

The signals stored on the interior CAN by the corresponding door control units are passed on on the chassis CAN by the central gateway control unit (N93). After the AIRMATIC with ADS control unit wakes up the current vehicle level is checked and corrected if necessary. Level control is performed in wake-up mode, e.g. by loading and unloading the vehicle without the AIRmatic compressor unit (A9/1) being connected. By activating the AIRMATIC with ADS control unit a chronological advance occurs which is used to correct the vehicle level. This reduces the amount of time which passes before level correction is performed, and also increases the availability of the vehicle.

If the AIRMATIC with ADS control unit detects a critical condition for example, such as a too low vehicle level at the front axle, which means that the full wheel angle can no longer be guaranteed, it transmits the appropriate fault message to the central gateway control unit via the chassis CAN. The central gateway control unit makes it available to the instrument cluster (A1) on the central CAN (CAN F). As a result of this the message "Please wait for a short time - vehicle is lifting up" is displayed in the multifunction display (A1p13) of the instrument cluster.

Lifting up out of the critical condition also takes place when the on-board electrical system is initially not adequate for this. The front SAM control unit with fuse and relay module (N10/1) evaluates the voltage of the on-board electrical system continuously and interrupts or prevents the lifting process if necessary. Current-intensive consumers are shut down in a fixed sequence until a predetermined minimum voltage is reached again.

Additional function requirements for compressed air supply
^ Circuit 61 ON, n > 300 rpm

Compressed air supply function sequence
Under normal operating conditions, the AIRmatic system operates with different pressures depending on the load.

Compressed air is supplied by the AIRMATIC compressor unit. Any surplus compressed air which is generated is stored in the AIRMATIC central reservoir. This allows large quantities of compressed air to be made available quickly. This increases the adjustment speed when lifting the vehicle and also permits a control when the engine is switched OFF.

If a too low pressure is detected in the AIRMATIC central reservoir while driving, the AIRMATIC compressor unit as well as the AIRMATIC central reservoir charge valve (Y36/6y5) are actuated and compressed air is delivered to the central reservoir. If the required pressure is reached, the AIRMATIC compressor unit is switched off and the AIRMATIC central reservoir charge valve is closed.

The function is active as of a speed of v > 40 km/h (during acceleration) and up to a speed of v > 20 km/h (during braking). The upper cutoff pressure for central reservoir charging depends on the current atmospheric pressure. Information on this is provided by the CDI control unit (N3/9) (model 221 with diesel engine) or by the ME-SFI control unit (N3/10) (with gasoline engine) on the chassis CAN. The pressure in the AIRMATIC central reservoir is monitored by the AIRMATIC pressure sensor (Y36/6b1).

The compressed air is distributed via the level control valve unit (Y36/6) to the air suspension bellows of the suspension struts. The following components are accommodated in the level control valve unit:
- AIRMATIC pressure sensor
- Left front level control valve (Y36/6y1)
- Right front level control valve (Y36/6y2)
- Left rear level control valve (Y36/6y3)
- Right rear level valve (Y36/6y4)
- AIRmatic central reservoir charge valve

Additional function requirements for level control
^ Circuit 61 ON, n > 300 rpm

Level control function sequence
Level control is realized by means of 4 suspension struts with integral bellows.

If compressed air is admitted to an air suspension bellows, the vehicle level at the wheel in question increases. Conversely, the vehicle level decreases if compressed air is released via the corresponding level control valve or via the AIRMATIC pressure reduction valve (A9/1y1).

To compute the current vehicle level the signals from the following components are read in directly by the AIRMATIC with ADS control unit:
- Rear axle level sensor (B22/3)
- Left front level sensor (B22/8)
- Right front level sensor (B22/9)

By operating the level control switch (S6/2s10) in the cockpit switch group (S6/2) the driver can select between the normal level and raised level, each operation of the level control switch causing a change to another level in each case. The status of the level control switch is read in by the upper control panel control unit (N72/1) via the instrument panel LIN (LIN 1) and provided on the interior CAN. The central gateway control unit makes it available to the AIRMATIC with ADS control unit on the chassis CAN. The function indicator in the level control switch is actuated by the AIRMATIC with ADS control unit in the opposite direction.

The values listed in the following of the levels and transient conditions can deviate from each other depending on the variant.

Level:
- Higher level
- Comfort performance map: 30 mm
- Sport performance map: 30 mm

- Normal level
- Comfort performance map: 0 mm
- Sport performance map: 0 mm

- Lowered level 1
- Comfort performance map: -10 mm
- Sport performance map: -20 mm

- Lowered level 2
- Comfort performance map: -20 mm
- Sport performance map: -20 mm

Transition conditions:
- from raised level to normal level
- v > 120 km/h or
- v > 80 km/h for t > 3 min

- from normal level to lowered level 1
- Comfort performance map: v > 120 km/h
- Sport performance map: v > 100 km/h

- from lowered level 1 to lowered level 2
- Comfort performance map: v > 160 km/h
- Sport performance map: v > 140 km/h

- from lowered level 2 to lowered level 1
- Comfort performance map: v < 120 km/h
- Sport performance map: v < 100 km/h

- from lowered level 1 to normal level
- Comfort performance map: v < 80 km/h
- Sport performance map: v < 60 km/h

Lock position function sequence
So that when intentionally lifting the vehicle, e.g. with a vehicle jack, compressed air is not drained permanently from the air suspension bellows, in order to lower the vehicle, it is required to recognize this reduction in wheel load automatically and to derive a blocking position from it. The blocking position is a pure software application which prevents actuation of the level control valves (drain process). If the blocking position is recognized by the AIRMATIC with ADS control unit, no display in the instrument cluster and no fault storage takes place. As soon as the ESP control unit (N47-5) makes available information on wheel speeds at the front wheels, the AIRMATIC with ADS control unit cancels the blocking position and starts with the level control. The output stages of the AIRMATIC with ADS control unit are actuated via diagnosis independently of the blocking position status, i.e. it is always possible.

Additional function requirements for damper adjustment
^ Circuit 61 ON, n > 300 rpm

Damper adjustment and chassis adjustment function sequence
The AIRMATIC system has automatic damper adjustment which works according to the "Skyhook" algorithm. All driving condition data are collected and evaluated in the AIRMATIC with ADS control unit and from this the actuation signals for damper adjustment are generated. The damping is adjusted harder or softer depending on the driving situation. The AIRMATIC with ADS control unit reads in the signals from the following components directly to determine the movement direction of the vehicle body:
- Left front level sensor
- Right front level sensor
- Rear axle level sensor

Furthermore the following information is provided to the AIRMATIC with ADS control unit via the chassis CAN:
- Status of service brake
- Wheel speed and wheel rotation direction on front left and right
- Data from tire pressure loss warning from ESP control unit, except code (475) Tire pressure monitor (Premium)
- Vehicle speed (substitute value), from instrument cluster
- Engine torque, from CDI control unit (model 221 with diesel engine) or from ME-SFI control unit (with gasoline engine)
- Steering wheel angle and steering angle rate of change, recorded by steering angle sensor (N49) and steering column tube module (N80)

The AIRMATIC with ADS control unit computes the required damping force individually for each wheel from the incoming information.

There are 2 different damper operating modes:
- Soft damping (valves energized)
- "Skyhook" mode (valves in control mode)

The left front axle damping valve unit (Y51), right front axle damping valve unit (Y52), left rear axle damping valve unit (Y53) and right rear axle damping valve unit (Y54) are actuated directly according to the selected damper operating mode. Soft damping is selected individually for each wheel (if the degree of vehicle excitation permits this). If the vehicle excitation exceeds a certain degree, "Skyhook" damping is activated for the appropriate wheel. If the vehicle excitation has decayed, the system switches back to soft damping.

If the sensor system records a sporty driving style for example, the comfortable basic damping becomes harder automatically.

The control characteristics and control response of the damper adjustment can be influenced by the driver in the process by operating the chassis adjustments switch (S6/2s15) in the cockpit switch group.

In the process he has the choice between:
- Comfort (switch not operated): Light-emitting diode (LED) OFF
- Sport (switch operated): LED ON
- Comfort (switch operated again): LED OFF

The signal for the selected suspension adjustment reaches the AIRMATIC with ADS control unit from the chassis adjustments switch via the following path:
- Instrument panel LIN
- Upper control panel control unit
- Interior CAN
- Central gateway control unit
- Chassis CAN

The signal for actuating the function LEDs in the chassis adjustments switch takes place through the AIRMATIC with ADS control unit in the opposite direction. When the engine is started again the chassis adjustment stored previously is carried out. The damping at all 4 wheels is adjusted soft when the vehicle is at a standstill. Only when a defined minimum speed is exceeded does the system change over to "Skyhook" mode.

In addition a braking or accelerating process which is starting influences the damper operating mode towards "hard", in order to avoid the pitching tendencies of the vehicle. If system components (e.g. valves or sensors) fail, the system automatically switches back to the fallback level "hard" (deenergized valves).

System and warning messages function sequence
System and warning messages with handling instructions for the driver can be output via the multifunction display in the instrument cluster.

To output the messages the AIRMATIC with ADS control unit transmits corresponding information on the chassis CAN The central gateway control unit makes it available to the instrument cluster on the central CAN.

Fault and warning messages are displayed according to a fault priority.

Texts displayed in instrument cluster:
- "Stop, car too low", in addition signal tone F1
- "Please wait for a short time, VEH is lifting up", in addition signal tone F2
- "Nonfunctional", no signal tone F3
- "Vehicle is lifting up", no signal tone M1

Priority classes: F1 = high priority, M1 = low priority. If several faults exist at the same time, several messages can be displayed.