Air Body Control, Function - GF32.22-P-0004RF
Model 253 with code 489 (AIR BODY CONTROL)
Block diagram
Function requirements, general
- Engine running
- Drive train operational
System in general
The AIR BODY CONTROL system is a combination of a multi-chamber air suspension with continuous damper adjustment, in which both the damping ad the suspension are adapted on a wheel basis. The system is made up of the following sub-functions:
- Wake-up mode, function
- Air suspension, function
- Variable damping, function
- Lower/raise rear end function
- Locking position, function
- System and warning messages, function
Wake-up mode, function
The AIR BODY CONTROL, 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. 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 AIR BODY CONTROL, 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. Activation of the AIR BODY CONTROL, control unit creates a chronological lead, 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. The AIR BODY CONTROL electric compressor is used to supply pressure. The AIR BODY CONTROL compressor is activated by the AIR BODY CONTROL, control unit through the AIR BODY CONTROL relay.
The duty cycle is monitored to protect against overload. Once the maximum operating time has been reached, the AIR BODY CONTROL compressor is switched off and enters a cooling phase. The excess compressed air in the air suspension bellows is reduced through actuation of the AIR BODY CONTROL pressure relief valve. The AIR BODY CONTROL, control unit is sent the atmospheric pressure and the intake air temperature for actuation of the compressed air supply over the chassis FlexRay and the drive train CAN using the powertrain control unit interface from the ME-SFI [ME] control unit (with gasoline engine) or the CDI control unit (with diesel engine).
The level control is realized by 4 multiple-chamber air suspension bellows. The multiple-chamber air suspension bellows consist of several air chambers, which are connected or disconnected to each other by switching the air suspension valves. This makes it possible to switch between different spring characteristics.
If the AIR BODY CONTROL compressor pumps air through a corresponding valve in the AIR BODY CONTROL valve unit into one of the multiple-chamber air suspension bellows, the vehicle level is raised at the affected wheel. Conversely, the vehicle level decreases when air from the multiple-chamber air suspension bellows is released by the corresponding valve in the AIR BODY CONTROL valve unit and released at the AIR BODY CONTROL pressure reduction valve in the AIR BODY CONTROL compressor. The driver can adjust the vehicle level by pressing the vehicle level button in the left lower control panel (with automatic transmission) or in the right lower control panel (with manual transmission).
The signals from the vehicle level button are read in by the left lower control panel (with automatic transmission) or by the right lower control panel (with manual transmission). The left lower control panel or the right lower control panel sends the signal via the LCP LIN, the Audio/COMAND control panel, the telematics CAN, the head unit, the user interface CAN, the electronic ignition lock control unit and the chassis FlexRay to the AIR BODY CONTROL, control unit. The AIR BODY CONTROL, control unit sends a request over the chassis FlexRay to the AIR BODY CONTROL Plus control unit, which then actuates the individual air suspension valves.
The wheel speeds are determined by the left front axle RPM sensor, right front axle RPM sensor, left rear axle RPM sensor and right rear axle RPM sensor and directly read in by the Electronic Stability Program control unit.
| Vehicle levels | |||
|---|---|---|---|
| Level designation | Level [mm] | v [km/h] | Comment |
| Comfort | -7 -15 |
< 180 > 180 |
Raise to -7 mm at v < 180 km/h |
| Sport | -16 | - | - |
| SPORT PLUS | -16 | - | - |
| Raised level (EN) | +30 | - | Lower to -7 mm at v > 60 km/h and 3 min Lower to -7 mm at v > 70 km/h |
Variable damping, function
The electronically regulated, continuous damping system operates fully automatically. In comparison to the conventional suspension, it provides improved driving comfort and driving safety. Damping is set harder or softer by the electronics of the AIR BODY CONTROL, control unit or the AIR BODY CONTROL Plus 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 the left lower control panel (with automatic transmission) or from the right lower control panel (with manual transmission). The signals of the DYNAMIC SELECT switch are read in by the left lower control panel (with automatic transmission) or by the right lower control panel (with manual transmission). The left lower control panel (with automatic transmission) or the right lower control panel (with manual transmission) sends the signal over the LCP LIN, the Audio/COMAND control panel, the telematics CAN, the head unit, the user interface CAN, the electronic ignition lock control unit and the chassis FlexRay to the AIR BODY CONTROL, control unit. The LEDs are actuated in the opposite direction.
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 AIR BODY CONTROL, 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 AIR BODY CONTROL, control unit uses the signals from the left front body acceleration sensor, the right front body acceleration sensor and the rear left body acceleration sensor to calculate the body acceleration and the body speed of the vehicle.
Based on the input signals, the AIR BODY CONTROL, 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.
Function requirements for lowering/raising rear end function
- Parking brake engaged
- Gear range "P" engaged
Lower/raise rear end function
To make it easier to load/unload the vehicle, the rear area of the vehicle can be lowered. To do so, the rear-end lowering switch is installed at the left in the trunk.
To lower the vehicle the rear-end lowering switch must be briefly pulled. The indicator lamp in the rear-end lowering switch starts to flash until the rear end of the vehicle has dropped by 40 mm. After this the indicator lamp lights up permanently.
The AIR BODY CONTROL, control unit reads in the signal of the rear-end lowering switch directly and actuates the AIR BODY CONTROL valve unit. The vehicle level is reduced by releasing air from the multiple-chamber air spring bellows. Air is removed through actuation of the left rear level control valve and the right rear level control valve in the AIR BODY CONTROL valve unit and the AIR BODY CONTROL pressure relief valve in the AIR BODY CONTROL compressor. The lowering procedure is interrupted, when
- A door is opened.
- The vehicle is driven at a speed in excess of 2 km/h.
The vehicle is automatically set back to the height for the last selected transmission mode, when the vehicle is driven faster than 2 km/h. To raise the vehicle the rear-end lowering switch must be briefly pulled. The indicator lamp in the rear-end lowering switch goes out and the vehicle is raised by 40 mm.
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 AIR BODY CONTROL, control unit, nothing is displayed in the instrument cluster and no faults are stored.
The locking position is automatically canceled if the AIR BODY CONTROL, control unit receives wheel speed signals from the left front and right front with v>10 km/h from the Electronic Stability Program control unit via chassis FlexRay. The level control functions are then reactivated.
The output stage actuations of the AIR BODY CONTROL, control unit through the diagnosis take place independent of the locking status and are thus always possible.
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 AIR BODY CONTROL, control unit sends appropriate messages to the instrument cluster over 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
- The rear-end lowering switch is pulled again.
| Electrical function schematic for AIR BODY CONTROL | PE32.32-P-2053-97FBA | ||
| Overview of system components of AIR BODY CONTROL | GF32.22-P-9993RF |