Diagnosis
ABC valve units
N51/2
Receiving sensor signals, calibrating sensors and monitoring sensors
Suspension, damping
1. Detecting vehicle handling (vertical, longitudinal and lateral acceleration of body, plunger movement, braking and comfort/sport switchover)
2. Calculating damping forces
Level control and adjustment
1. Detecting vehicle level and driver's preferences (switch position)
2. Calculating desired level
Monitoring control module, operating conditions and control signals
Fault identification, cutout, type of fault, diagnosis entry
Converting damping forces and specified level into operations of the valves
Output stages
Driver request level
Vehicle level
Vertical body acceleration
Longitudinal and lateral acceleration
Vehicle speed
Comfort/
SPORT
switchover
Suction restrictor valve
System pressure
Movement Plunger
Oil tempe-rature
The ABC control module is split up functionally as follows:
Signal conditioning
Function logic component
Safety circuit
Signal conditioning
The following input signals are processed by the function logic component for calculations or as 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
- Signal from longitudinal acceleration sensor
- Signal from lateral acceleration sensor
Calculation of pitch movements
- Signal from longitudinal acceleration sensor
Calculation of roll movements
- Signal from lateral acceleration sensor
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Calculation for valve control
- Signal of left, right front axle level
- Signal of left, right rear axle level
- Signal of movement of left, right front axle spring strut
- Signal of movement of left, right rear axle spring strut
Calculation of actuation of ABC suction restrictor valve
- System pressure signal
Calculation of vehicle level
- Signal from level sensors at each wheel
Information signals (control)
- Signal from comfort and SPORT switch
- Signal from level control switch
- Signal from door contact switch, trunk, remote control
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Function logic component
The conditioned input signals are processed in the logic component and converted into output signals.
Signal from front left, front right and rear right 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
- Vehicle status. A distinction is made between the vehicle when driven and
when stationary. Incorrect wheel speed signals are also detected.
Signal from level sensors (B22/7, B22/8, B22/9, B22/10):
The front left, front right, rear left and rear right level sensors supply a signal which detects the distance between the middle of the wheel and the body at each wheel.
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Signal from comfort and SPORT switch or ABC SPORT switch (N72/1s3 or N72s20):
The signal from the comfort and SPORT switch provides information regarding the choice between comfort-oriented and a sporty map. The driver's preferred settings are stored until changed by the driver (even with Ignition OFF).
Signal from level adjustment switch (N72/1s2 or 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 stage 1
- Raised level stage 2
The driver's preferred settings are stored until changed by the driver (even with Ignition OFF).
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Wake-up function
A parked vehicle is "woken up" before the engine is started, in other words the ABC control module recognizes that a trip may be upcoming by means of the signals from the door contact switches, the trunk switch and the remote control. The momentary vehicle level is checked and the vehicle is lowered, if necessary, to the normal level. It is not possible to raise the vehicle. In addition, various system functions are checked. For example, the valves are initialized in order to carry out all the actuations immediately after the engine is started. Waking up the ABC control module (e.g. by opening a door) offers a time lead which is used for an immediate correction of the vehicle level. This reduces the waiting time required to correct the vehicle level and the vehicle is ready for driving more promptly.
Supply pressure control
The control parameter is the system pressure. The quantity drawn in by the radial piston pump is controlled, as necessary, by means of the suction restrictor valve.
Function of level control and adjustment
The control module analyzes the driver request by means of the setting of the level adjustment switch and the vehicle speed in order to set the correct vehicle level by means of the relevant control valves of the spring struts in line with the vehicle load.
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Suspension function
The control module determines the particular optimal suspension and damping characteristics from the level positions, the vertical body accelerations as well as the longitudinal and lateral acceleration of the vehicle, and the vehicle speed.
The oil flow can be controlled at each wheel in line with the particular requirements by operating the control valves positioned at each wheel.
Locking function
The shut-off valves which are closed when de-energized, and which are connected in series to the control valves of the spring struts, are part of the system safety function. They additionally prevent the parked vehicle from lowering because of residual leakage of the control valves.
If the control module detects that no load exists at all the wheels when the vehicle is stationary and the engine switched off, the shutoff valves of the spring struts are closed and the control valves are no longer operated. The vehicle therefore remains at the current level. This is essential, for example, when changing a wheel or during repair work (lifting platform).
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Safety circuit
After the engine is switched on, and during operation, the ABC control module monitors all the essential components of the system. 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 partially or fully switched off and this is indicated to the driver by means of the multifunction display in the instrument cluster.
A fault code is stored in the control module. The function is only partially switched off depending on the fault.
The safety circuit also constantly monitors the battery voltage. If the voltage drops below 9 V or rises above 16.5 V, the system is likewise switched off until the voltage is again within the specified range.