Airmatic

Description - WIS 32.22 Air Suspension / Airmatic

The W220 Airmatic system is a fully supporting air suspension system which provides both static and dynamic support by means of four air bellows or struts located at the wheels. Each strut has an air bag and a dampener built-in the one unit. The struts get air from an air compressor located behind the front bumper close to the front wheel well. On the opposite side is the central reservoir which supplies pressure via pressure lines and a valve unit. The valve unit is connected to a computer which monitors the air pressure, the vehicle weight, the vehicle height requirement and vehicle stance (angle) and then sets the ride height accordingly.

Features - Airmatic

• Level control both manual and speed sensitive.
• Electronic level control which maintains a constant even level at the front and rear axles according to the driving and vehicle load conditions.
  • When the vehicle is stationary the level is readjusted if there is a difference of more than +/- 10mm after a door or the trunk lid is opened.
  • While driving the level is readjusted if there is a difference of more than +/- 20mm. The level is adjusted to +/- 10 mm every 15 minutes.
• Active Damping System (ADS) which changes the damping forces according to the road conditions and the driver's driving style. The road conditions are determined by vertical acceleration sensors in the body of the vehicle. The horizontal acceleration is determined by measuring the vehicle speed and turn angle.

Advantages - Airmatic

Higher level of driving safety and ride comfort due to:

• Adapting damping to road conditions and driving style.
• Low location of centre of gravity as vehicle lowers above 70KPH.
• Low aerodynamic drag and fuel consumption as vehicle lowers above 70KPH.
• Less tendency for vehicle to lift at speed.

Individual adaptation due to:

• Raising vehicle level for poor road surfaces and when negotiating driveways.
• Two possible damping levels for comfort or sport driving styles in vehicles produced up to 08/99.
• Three possible damping levels for comfort, sport or extreme sport driving styles in vehicles produced after 09/99.

Driver information due to:

• Vehicle level displayed by indicator lamps and switches.
• Warning messages in multi-function display if vehicle is too low.

 

Function

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 main 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 control 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.

• Signal from level sensors (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).

• Brake 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.

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

• Signal from level adjustment switch (N72/1s2):
  • 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

• 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. Phased in as of 09/00, the damping is set to the Sport 1 damping level if the vehicle speed is >160 km/h.

• Level control and 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 control 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 spring struts are supplied directly by the air compressor.

• Main reservoir pressure control
  • The main control parameters are the pressure in the main reservoir, the outside air pressure and the vehicle speed.

• 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 up" before the engine is started. That is to say, the AIRmatic with ADS control module receives signals from the door contact switches, the trunk switch and infrared remote control indicating that the driver may soon 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 car 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 main 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 function

If the control module detects that all wheels are unloaded when the vehicle is stationary, the valves of the sprint 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 safety circuit detects faulty signals from sensors, faults in the control module and in the electric line 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 control is partially switched off depending on the fault that occurred. The system always strives to maintain the selected vehicle level. Moreover, the safety circuit continuously 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.

 

Pressure supply function

• 42 - AIRmatic central reservoir
• A9/1 - AIRmatic compressor unit
• Y36/6 - Level control valve unit

In normal driving mode, AIRmatic works with a pressure of between 6 and 10 bar depending on the load. An electrical compressor is used to supply pressure. This is installed in the AIRmatic compressor unit (A9/1).

In addition the system has an AIRmatic central reservoir (42) which stores the compressed-air. The reservoir pressure is between 13 and 16 bar (at sea level). The system is either supplied with pressure via the AIRmatic central reservoir or via the air compressor.

Level control function

The AIRmatic at the front and rear axle is a fully supporting suspension system. It keeps the vehicle level constant when the engine is running irrespective of the load. At the same time air from the air compressor is delivered to the spring struts via the valve unit until the vehicle level has been adjusted. The vehicle level at the front axle is recorded by two level sensors at the rear axle and conveyed to the AIRmatic with ADS control module. The level at the individual spring struts is controlled by four level valves in the valve unit and a pressure relief valve on the AIRmatic compressor unit.

An AIRmatic central reservoir for compressed air also enables the vehicle level to be controlled when the engine is not running. In addition the adjustment of the vehicle level is decoupled from the air compressor.

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.

Normal function (engine running)

When the vehicle is stationary the level is readjusted if there is a difference of more than +/- 10 mm after a door or the trunk lid is opened.

While driving the level is readjusted if there is a difference of more than +/- 20 mm. The level is adjusted to +/- 10 mm every 15 minutes.

Depending on the situation, pressure can be generated by the compressor or the pressure supply of the AIRmatic central reservoir can be used to raise the vehicle. When the vehicle is stationary the pressure from the reservoir is used for noise reasons. Pressure can also be supplied from the compressor and AIRmatic central reservoir at the same time when there is a particularly high pressure demand.

The lowering of the vehicle level is recognized by the control module from the level sensors when loading the vehicle. By actuating solenoid valves air is delivered to the spring struts of the particular front wheel or rear axle until the vehicle has reached its specified value. In addition the pressure relief valve is opened to actuate the respective wheel valve when unloading the vehicle.

Wake-up function (operating period approx. 1 minute)

The AIRmatic with ADS control module is "woken up" using the remote control, door contact switches or trunk illumination switch in order to check the current vehicle level for critical conditions (level too low) and if necessary to raise the vehicle or lower it when unloading. If the vehicle level is lowered by more than 30 mm, it is raised to the normal level by the reservoir (only with a reservoir pressure > 11 bar). At a vehicle level of < -65 mm and even at a reservoir pressure of <11 bar it is raised out of the "critical range" by the compressor to -63 mm (condition: battery voltage > 12.4 V).

If the vehicle level is raised by more than 10 mm when unloading, it is lowered to the normal level by relieving the pressure.

The vehicle cannot be raised by the level control switch.

Function in vehicle condition "Ignition ON"

The same function as for the wake-up function, but without time limit.

Run-on function (operating period approx. 1 minute)

After "ignition OFF" the control module performs changes in the level in order to be able to readjust the vehicle level (raise or lower) during any loading or unloading operations. (The same function as for the wake-up function).

Components

AIRmatic, location of electrical/electronic components:

• A9/1 - AIRmatic compressor unit
• A1p13 - Multifunction display
• B7 - AIRmatic pressure sensor
• B22/3 - Rear axle level sensor
• B22/8 - Left front level sensor
• B22/9 - Right front level sensor
• B24/3 - Left front body acceleration sensor
• B24/4 - Right front body acceleration sensor
• B24/6 - Right rear body acceleration sensor
• K40/7 - Right front fuse and relay module
• kO - AIRmatic compressor relay
• N49 - Steering angle sensor
• N51 - AIRmatic with ADS control module
• N72/1s2 - Level control switch
• N72/1s3 - Comfort and sport switch
• S9/1 - Stop lamp switch
• X11/4 - Data link connector
• Y36/6 - Level control valve unit
• Y51 - Left front axle damping valve unit
• Y52 - Right front axle damping valve unit
• Y53 - Left rear axle damping valve unit
• Y54 - Right rear axle damping valve unit

AIRmatic, location of pneumatic/hydraulic components:

• 40 - Front spring strut
• 41 - Rear spring strut
• 42 - AIRmatic central reservoir
• A9/1 - AIRmatic compressor unit
• Y36/6 - Level control valve unit
• Y51 - Left front axle damping valve unit
• Y52 - Right front axle damping valve unit
• Y53 - Left rear axle damping valve unit
• Y54 - Right rear axle damping valve unit

 

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