AIRmatic Function - GF32.22-P-0002LFM
Model 222
as of model year 2018
Block diagram
Function requirements, general
- Engine running
- Drive train operational
System in general
The AIRmatic system is the combination of an air suspension with a continuous damper adjustment in which the dampening is adapted on a wheel by wheel basis corresponding to the road surface condition and driving style. The control algorithm for the dampening and level adjustment is filed in the AIRmatic control unit. Automatic selection of the operating range or characteristics in the steam power diagram is calculated on the basis of the various driving signals. The configured vehicle level is held constant, irrespective of the payload. Level sensors on each wheel measure the vehicle level. When loading the vehicle, the AIRmatic compressor pumps additional air into each of the spring bellows. When unloading, the vehicle level is adapted by venting air.
The AIRmatic compressor runs permanently during dampening and level controls.
The system is made up of the following subfunctions:
- Wake-up mode, function
- Air suspension, function
- Locking position, function
- Variable damping, function
- System and warning messages, function
Wake-up mode, function
The AIRmatic control unit is activated (woken up) by the active chassis FlexRay after the vehicle is unlocked in order to check the current vehicle level and correct it, if necessary. The level is regulated in wake-up mode, e.g. through loading/unloading the vehicle without activating the AIRmatic compressor when the AIRmatic central reservoir is sufficiently filled (in vehicles with 4MATIC, except code 494 (USA version)).
A critical condition, for example a too low vehicle level at the front axle, in which the full wheel angle can no longer be guaranteed, is detected by the AIRmatic control unit as a fault.
The driver is made aware of the situation by the message "Vehicle being raised, please wait" on the instrument cluster. Waking up the AIRmatic control unit immediately after unlocking the vehicle creates a chronological advance, which is used to correct the vehicle level. This reduces the amount of time which passes before level correction is performed, therefore increasing vehicle availability.
Air suspension, function
Under normal operating conditions, the air suspension operates with different pressures depending on the load. Pressure is supplied by the AIRmatic compressor. The AIRmatic compressor is activated by the AIRmatic control unit via the AIRmatic relay.
The compressed air is distributed to the individual suspension struts of the front axle and rear axle via the AIRmatic valve unit.
For vehicles with 4MATIC (except CODE 494 (USA version)) the AIRmatic system is equipped with a central reservoir which contains compressed air, to enable fast adjustment times for the vehicle level irrespective of compressor operation. The pressure in the AIRmatic central reservoir is monitored by the AIRmatic pressure sensor integrated in the AIRmatic valve unit. As soon as the pressure in the AIRmatic central reservoir drops below the threshold value, the AIRmatic compressor is activated.
Level control is realized by 4 air suspension bellows. If the AIRmatic compressor or the AIRmatic central reservoir (with 4MATIC, except CODE 494 (USA version)) pumps compressed air through each AIRmatic valve unit level control valve into an spring bellows, the vehicle level rises at the corresponding wheel.
Conversely, the vehicle level decreases when compressed air from the air suspension bellows is released by the corresponding valve in the AIRmatic valve unit and released at the AIRmatic pressure reduction valve in the AIRmatic compressor.
The driver can adjust the vehicle level by pressing the vehicle level button on the Audio/COMAND control panel (with code 448 (Touchpad)) or on the lower control panel (with code 446 (Touchpad only)).
In vehicles with code 448 (Touchpad), the actuation signal of the vehicle level button is read in by the Audio/COMAND control panel.
The Audio/COMAND control panel sends the signal via the telematics CAN, the head unit, the user interface CAN, the electronic ignition lock control unit and the suspension FlexRay to the AIRmatic control unit. In vehicles with code 446 (Touchpad only), the actuation signal of the vehicle level button is read in by the lower control panel. The lower control panel sends the signal via the LCP LIN, the touchpad, the telematics CAN, the head unit, the user interface CAN, the electronic ignition lock control unit and the suspension FlexRay to the AIRmatic control unit.
The wheel speeds are determined by the left front axle rpm sensor and the right front axle rpm sensor and read in directly by the Electronic Stability Program control unit.
| Vehicle levels | |||
|---|---|---|---|
| Level designation | Level [mm] | v [km/h] | Comment |
| Comfort | 0 | v ≤ 125 | Lower to -10 mm at v > 125 km/h |
| -10 | v > 125 | Raise to 0 mm at v ≤ 80 km/h | |
| -20 | v > 160 | Raise to -10 mm at v ≤ 120 km/h | |
| Sport | -10 | v ≤ 120 | In Sport mode the vehicle always has a level of -10 mm up to 120 km/h. |
| -20 | v > 120 | Raise to -10 mm at v ≤ 80 km/h | |
| Raised level (EN) | 30 | v ≤ 80 | The vehicle is lowered to normal level (NN) at v ≤ 80 km/h and t = 3 min. |
| 30 | v ≤ 120 | The vehicle is lowered to normal level at v ≤ 120 km/h. |
Locking position, function
To ensure that, when intentionally raising the vehicle (e.g. with a vehicle jack), air is not continuously released from the suspension struts (which would lower the vehicle), it is necessary to detect this reduction in wheel load automatically and then to initiate a locking position. The locking position is a pure software function which prevents the actuation of the level control valves (draining process). If the locking position is detected by the AIRmatic control unit, nothing is displayed in the instrument cluster and no faults are stored.
The locking position is automatically canceled when the AIRmatic control unit receives wheel speed signals of v > 10 km/h at the left front and right front wheel from the Electronic Stability Program control unit via the suspension FlexRay. The level control functions are then activated again.
The output stage actuations of the AIRmatic control unit via the diagnosis take place independent of the locking status and are thus always possible.
Variable damping, function
The electronically regulated, continuous damping system operates fully automatically. It provides improved driving comfort and driving safety, compared to the conventional steel suspension. Damping is set harder or softer by the electronics of the AIRmatic control unit depending on the driving situation. If the sensor system records a sporty driving style for example, the comfortable basic damping becomes harder automatically. This automatic program can be set by the driver via the DYNAMIC SELECT switch.
In vehicles with code 448 (Touchpad), the actuation signal of the DYNAMIC SELECT switch is read in by the Audio/COMAND control panel. The Audio/COMAND control panel sends the signal via the telematics CAN, the head unit, the user interface CAN, the electronic ignition lock control unit and the suspension FlexRay to the AIRmatic control unit.
In vehicles with code 446 (Touchpad only), the actuation signal of the DYNAMIC SELECT switch is read in by the lower control panel. The lower control panel sends the signal via the LCP LIN, the touchpad, the telematics CAN, the head unit, the user interface CAN, the electronic ignition lock control unit and the suspension FlexRay to the AIRmatic control unit.
The electronics works continuously within a broadly spread damping performance map. The damping force is adapted individually and automatically at each wheel to the current requirements, the road condition and the driving conditions.
As a result, the vehicle rolls smoothly even on poor road surfaces, without impairing driving stability. The AIRmatic control unit uses the left front level sensor, right front level sensor, left rear level sensor and right rear level sensor to determine the current vehicle level and shock absorber speeds.
The AIRmatic control unit uses the signals of the left front body acceleration sensor, the right front body acceleration sensor and the right rear body acceleration sensor to calculate the body acceleration of the vehicle.
Based on the input signals, the AIRmatic control unit determines the optimum damping stage for each shock absorber and directly actuates the left front axle damping valve unit, right front axle damping valve unit, left rear axle damping valve unit and right rear axle damping valve unit accordingly. These can be adjusted for each wheel, i.e the damping can be adjusted continuously at each individual wheel.
System and warning messages, function
System and warning messages with safety and system-relevant instructions for the driver are displayed on the instrument cluster. In order to output the messages, the AIRmatic control unit sends appropriate messages to the instrument cluster via the chassis FlexRay, the electronic ignition lock control unit and the user interface CAN. There are various system and warning messages with different fault priorities, depending on the severity of the fault and the urgency of the request for action to be taken.
If several faults exist at the same time, several fault messages will be output accordingly.
Texts displayed in instrument cluster:
- "STOP, vehicle too low", plus an acoustic signal
- "Vehicle being raised, wait briefly"
- "Fault", no signal tone
The following system message is also displayed in the instrument cluster:
- "Vehicle lifts up", no signal tone
| Electrical function schematic for AIRmatic | PE32.32-P-2052-97SEB | ||
| Overview of system components for AIRmatic | GF32.22-P-9994LF |