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

Models 211, 240 

Fig 1: AIRmatic With ADS Control Module, Function Diagram

The functions of the AIRmatic with ADS control module are divided as follows:

• Signal conditioning
• Function logic component
• Safety circuit

Signal conditioning 

The following input signals are processed by the function logic component and used for calculations or to provide information:

• Calculation of body vertical acceleration
  • Signal from body acceleration sensors
• Calculation of vehicle speed
  • Wheel speed signal
  • Speed status signal
• Calculation of longitudinal and lateral acceleration
  • Wheel speed signal
  • Signal from steering angle sensor
• Calculation of compressor control
  • Outside temperature, outside air pressure signal
  • Reservoir pressure signal
  • Vehicle speed signal
  • Vehicle level signal
  • Duty cycle
• Calculation for valve control
  • Level signal from left front axle, right front axle
  • Rear axle level signal
• Calculation for control of central reservoir charge valve
  • Level signal from left front axle, right front axle Rear axle
  • Pressure signal
• Calculation of vehicle level
  • Signal from level sensors
• Information signals (control)
  • Signal from stop lamp switch
  • Signal from comfort and sport switch
  • Signal from level adjustment switch
  • Signal from door contact switch, trunk, remote control

Function logic component 

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

• Signal from body acceleration sensors (B24/3, B24/8, B24/9):

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

• Front wheel speed signal, left and right:

  Using the wheel speed signal, the ESP control module calculates

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

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

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

  Both front axle level sensors each supply 2 signals. The sensors detect and transfer the distance between the wheel center and the body at both the left and right-hand side of the vehicle.

  The rear axle level sensor supplies 2 signals. The sensor detects and transfers the distance between the wheel center and the body (average calculated from left and right wheel).

• Stop lamp switch signal (S9/1):

  When the driver presses the brake pedal, a signal is received by the ADS logic component and the damping at all wheels is set to "hard". The pitch motion of the vehicle when braking can therefore be reduced.

• Signal from comfort and sport switch (N72s25):

  The comfort and sport switch signal informs the system about the selection made by the driver between one comfort-oriented and 2 sporty damping maps. The "comfort" setting maintains the damping within the comfortable range as far as the driving style and road conditions will allow. The "Sport 1" setting makes the damping somewhat "harder". The "Sport 2" setting immediately sets the damping force to "hard". The driver's preferred settings are stored until changed by the driver (even with Ignition OFF). In the "Sport 1 and 2" settings the vehicle is also to the lowered vehicle level - 15 mm (USA 0 mm)

• Level adjustment switch signal (N72s18):

  The control module uses the signals from the level adjustment switch to determine the driver's preferences for the vehicle level:

  • Normal level
  • Raised level

  The driver's preferred settings are stored until changed again by the driver (even with ignition OFF) or until the vehicle exceeds specified speed thresholds.

• ADS II

  The control module uses the vertical body acceleration, longitudinal and lateral acceleration of the vehicle and the ground speed to determine the optimum level of damping.

  4 different damping forces can be set at each wheel by controlling the damping valves located at each wheel.

  The damping is set to the Sport 1 damping level if the vehicle speed is >160 km/h.

• Level adjustment

  The control module uses the setting of the level adjustment switch selected by the driver and the ground speed of the vehicle to control the appropriate level control valves and to set the correct vehicle level according to the vehicle load.

  The AIRmatic system is equipped with a pressure reservoir to keep the level adjustment time as short as possible (e.g. after loading). The reservoir pressure is used only when required in order to prevent filling the reservoir too often. This happens, for example if the vehicle level falls below a critical level when loading the vehicle or if the driver has set the vehicle level to "raised level". Pressure from the reservoir is also used when the vehicle is stationary to minimize noise. With normal control when the vehicle is moving, the suspension struts are supplied directly by the air compressor.

• Controlling the spring rate

  Additional volume is assigned to each suspension strut which can be made available or restricted according to the driving situation. This additional volume is available during normal driving conditions (greater degree of comfort).

• Central reservoir pressure control

  The control parameters are predominantly the pressure in the central reservoir, the outside air pressure and the speed of the vehicle.

• Compressor control

  The compressor is controlled via a relay. Since the compressor is not designed for continuous operation, the absolute running time and cooling phase are monitored to avoid overloading the compressor.

• Wake-up function

  A parked vehicle is "woken" before the engine is started, i.e. the AIRmatic with ADS control module receives signals from the door contact switches, the trunk switch and the infrared remote control which indicate that the driver may soon wish to start the engine and drive the vehicle. The current vehicle level is checked immediately and corrected if required. The vehicle level at the front axle is considered to be critical, for instance, if the full wheel angle can no longer be guaranteed. In this case a message appears on the multifunction display in the instrument cluster to warn the driver: "Stop vehicle too low". 

  If the control module is woken (for example by opening one of the doors), there follows a period of spare time before the driver actually starts the engine during which the vehicle level is corrected. This reduces the waiting time required to correct the vehicle level and the vehicle is ready for driving more promptly.

  Pressure in the central reservoir is used to raise the stationary vehicle. The compressor is only used if the pressure reservoir is empty. It must be ensured that the battery voltage is sufficient to then start the engine.

• Locking position, function

  If the control module detects that all wheels are unloaded when the vehicle is stationary, the valves of the suspension struts are closed. The vehicle therefore remains at the current level. This is essential, for example, when changing a wheel or during repair work (lifting platform).

  Safety circuit 

  The AIRmatic with ADS control module monitors all the important components of the system after they are switched on and during operation. The task of the safety circuit is to identify erroneous signals from the sensors and faults in the control module and in the wiring system. If a fault is detected, the system is switched off and a message is displayed on the multifunction display in the instrument cluster to warn the driver.

  The damper valves for ADS are no longer controlled and remain set to the "hard" damping level (driving safety level).

  In addition, a fault code is stored in the control module. The level adjustment function is only partially switched off depending on the fault. The system always strives to maintain the selected vehicle level.

  The safety circuit also constantly monitors the battery voltage. If the voltage falls below 10.5 V or exceeds 17.5 V, the system is switched off until the voltage returns to the specified range.