AIRmatic control module with ADS function - GF32.22-P-4200-02A

Fig 1: Compressor Unit Function Block Diagram

The AIRmatic with ADS control module is broken down into the following functions:

• Signal conditioning
• Function logic section
• Safety circuit

Signal conditioning 

The following input signals are processed by the function logic section for calculation or information purposes:

• Calculation of vertical body accelerations
  • Body acceleration sensors signal
• Calculation of vehicle speed
  • Wheel speed signal
  • Speed status signal
• Calculation of longitudinal and lateral acceleration
  • Wheel speed signal
  • Steering angle sensor signal
• Calculation of compressor actuation
  • Outside air temperature/outside air pressure signal
  • Reservoir pressure signal
  • Vehicle speed signal
  • Vehicle level signal
  • Operating time
• Calculation of valve actuation
  • Left/right front axle level signal
  • Rear axle level signal
• Calculation of AIRmatic central reservoir charge valve actuation
  • Left/right front axle and rear axle level signal
  • Pressure signal
• Calculation of vehicle level
  • Level sensors signal
• Information signals (operation)
  • Stop lamp switch signal
  • Comfort and sport switch signal
  • Level control switch, signal
  • Door contact, trunk, remote control switch signal

Function logic section 

The conditioned input signals are processed in the logic section and converted into output signals.

• Body acceleration sensors (B24/3, B24/8, B24/9) signal:

  The vertical acceleration of the vehicle is calculated from the signals from the body acceleration sensors.

• Left and right front wheel speed signal:

  The following are determined by the ESP control module by means of the wheel speed signal:

  • Vehicle speed
  • Longitudinal acceleration
  • Vehicle status. A distinction is made between a moving vehicle and a stationary vehicle. A defective wheel speed signal is also recognized.
• Steering angle sensor (N49) signal:

  The lateral acceleration of the vehicle is calculated using the steering angle sensor signal and the wheel speed signal.

• Level sensors (B22/8, B22/9, B22/3) signal:

  The two level sensors for the front axle each provide two signals which determine and convey the distance between the center of the wheel and the body on the right and left wheel separately. The level sensor for the rear axle provides 2 signals which determine and convey the distance between the center of the wheel and the body (mean value from the right and left wheel).

• Stop lamp switch (S9/1) signal:

  When the brake is operated a signal is recognized by the ADS logic section and the damping set to "hard" on all wheels. As a result the pitch motion of the vehicle can be reduced during braking.

• Comfort and sport switch (N72/1s3) signal:

  The signal from the comfort/sport switch provides information on the selection between a comfort-orientated and sporty map. In the "Comfort" setting damping is kept in the comfortable range as long as the driving style and road quality permits. In the "Sport" setting the damping changes more quickly towards "hard". The driver's requirement remains stored until it is revised again by the driver (even with ignition OFF).

• Level control switch (N72/1s2) signal:

  The control module recognizes the driver's requirement for vehicle level by means of the signal from the level control switch:

  • Normal level
  • Raised level

  The driver's requirement remains stored until it is revised again by the driver (even with ignition OFF) or set vehicle speed thresholds are exceeded.

• ADS II

  The control module determines the optimum damping stage in each case from the vertical body accelerations determined and the longitudinal and lateral acceleration of the vehicle and the vehicle speed.

  The 4 different damping force stages can be adjusted at each wheel by actuating the damping valve units which are assigned to the wheels.

• Level control and adjustment

  The control module adjusts the correct vehicle level depending on the load from the driver's required setting on the level control switch and from the vehicle speed via the respective level valves.

  So that the level control time remains as short as possible (e.g. after loading), the AIRmatic is equipped with a pressure reservoir. To avoid having to fill the reservoir too often, the reservoir pressure is only used when required. This occurs, for example, when a critical level is not reached when loading or when the driver requires the "raised level" setting. Also when the vehicle is stationary the pressure from the reservoir is used for noise reasons. The spring struts are supplied directly by the air compressor during normal control when driving.

• AIRmatic central reservoir pressure control

  The control variables are primarily: The pressure in the AIRmatic central reservoir, the outside air pressure and driving speed.

• Compressor actuation

  Actuation takes place via a relay. As the compressor is not designed to operate continuously the absolute operating time and cooling down phase is monitored to prevent overloading the compressor.

• Wake-up function

  A parked vehicle is "woken up" before starting, i.e. the AIRmatic with ADS control module recognizes that a journey may be imminent through signals from the door contact switches, trunk switch and IR remote control. The current vehicle level is checked immediately and corrected if necessary. For example, a vehicle level which is too low at the front axle, where full wheel lock can no longer be guaranteed, is assessed as a critical condition. In this case the driver is warned to "Stop - car too low"  by the multifunction display in the instrument cluster.

  When the control module is woken up, (e.g. due to a door being opened) there is a lead time which is used to correct the vehicle level immediately. This reduces the delay in correcting the level and the vehicle is therefore ready-to-drive in less time.

  The stationary vehicle is raised by the pressure in the AIRmatic central reservoir. The compressor is only used when the pressure reservoir is empty. It must be ensured that the battery voltage is high enough to then allow the engine to be started.

• Shut-off position function

  If the unloading of all the wheels when the vehicle is stationary is recognized by the control module, the spring strut valves are closed. The vehicle therefore remains at the current level. This is required when changing a wheel or for repair work (hoist) for example.

Safety circuit 

The AIRmatic with ADS control module monitors all the important components of the system after switching on and during operation. The task of the safety circuit is to recognize defective signals from sensors, faults in the control module and in the electrical wiring system. If a fault is recognized the system is switched off and this is displayed to the driver by the multifunction display in the instrument cluster. With ADS the damping valve units are no longer actuated and are in the hard damping stage (safe driving stage). A fault code is also stored in the control module. Depending on the fault, the level control is only partially switched off. The aim is always to maintain the set vehicle level.

The safety circuit also constantly monitors battery voltage. If the voltage of 10.5 V is not achieved or 17.5 V is exceeded, the system is also switched off until the voltage is within the specified range again.