GF32.50-P-0001RI Active Body Control (ABC), Function
GF32.50-P-0001RI Active body control (ABC), function
- with CODE (487) Active body control (ABC)
- as of model year 09
Active Body Control (ABC) in general
The ABC system is a full suspension system, i.e. the system is capable of applying active forces to each wheel with the aid of four hydraulic suspension struts.
The control intervention functions are effective up to a frequency range of approx. f = 5 Hz. For this purpose, the system requires an extensive sensor and actuator system which is evaluated, actuated and monitored by the ABC control unit (N51/2).
The ABC system contains the following sensors and actuators
- Left rear level sensor (B22/7)
- Left front level sensor (B22/8)
- Right front level sensor (B22/9)
- Right rear level sensor (B22/10)
- ABC lateral acceleration sensor (B24/12)
- Left front body lateral acceleration sensor (B24/3)
- Right front body acceleration sensor (B24/4)
- Left rear body lateral acceleration sensor (B24/5)
- Front axle ABC valve unit (Y36/1) with
- ABC pressure sensor (B4/5)
- Left front ABC pressure sensor (B4/8)
- Right front ABC pressure sensor (B4/9)
- Rear axle ABC valve unit (Y36/2) with
- Left rear ABC pressure sensor (B4/10)
- Right rear ABC pressure sensor (B4/11)
- ABC suction restrictor valve (Y86/1)
- Level adjustment switch (N72s18)
- ABC Sport switch (N72s20)
The active ABC suspension is different from other systems in that it uses dynamically-adjustable hydraulic cylinders at the wheels and does not use stabilizer bars as used in conventional suspensions.
The hydraulic cylinders are connected in series to the coil springs and generate forces through displacement, which counteract wheel load fluctuations.
This allows the rolling motion of the body to be fully compensated when cornering at up to maximum lateral acceleration. The ABC control unit continuously adapts the suspension and damping characteristic to the current driving condition.
The following values can be recorded with the aid of a sensor system:
- lateral acceleration,
- Vertical body acceleration
- relative travel between wheels and body level
- Pressure in the suspension struts
These actual values are constantly compared with the specified values and adapted accordingly.
Advantages of ABC system compared to conventional suspension:
- As a result of the active body damping, it is possible to use very soft, passive shock absorbers which improve vibration and tire comfort considerably.
- Despite the absence of stabilizer bars, the ABC system compensates the typical body roll when cornering and the pitch motion when accelerating or braking.
- Vibrations and shocks which are caused by road bumps can be damped more effectively.
- The selected handling characteristics are retained even in loaded condition.
The ABC system consists of the following subfunctions:
^ Wake up mode function sequence
^ Initial test function sequence
^ Level control function sequence
^ Pressure supply function sequence
^ Lock position function sequence
^ Suspension setting function sequence
^ System and warning messages function sequence
Wake-up mode function requirements
^ C. 15R On
Wake up mode function sequence
The ABC control unit is activated discretely by the driver SAM control unit (N10/10). The required data (signals from left door contact switch (S17/3), from right door contact switch (S17/4) when opening a door or from the locking pawl rotary tumbler switch (S88/4) when opening the trunk lid) are sent to the driver SAM control unit from the rear SAM control unit (N10/8) via the interior CAN.
The wake-up mode is canceled as soon as the engine is started and the ABC control unit changes into normal mode.
Initial test function requirements
^ C. 15R On
Initial test function sequence
In the initial check all the system tests summarized which are run through once after the system start.
The various tests forming the initial check are time-graded and performed according to requirement. All the components which are required for the function scope of wake-up mode, already have to be checked during the transition to wake-up mode.
The initial check is processed completely at the very latest after the engine has been started.
Level control function requirements
^ Circuit 61 ON
Level control function sequence
The ABC control unit actuates the following control valves to match the driving situation:
- Left front suspension strut control valve (Y36/1y1)
- Right front suspension strut control valve (Y36/1y3)
- Left rear suspension strut control valve (Y36/2y1)
- Right rear suspension strut control valve (Y36/2y3)
If oil flows through an activated control valve into a suspension strut, the vehicle level at the wheel in question is raised. Inversely, the vehicle level is lowered if oil flows from a suspension strut into the return circuit.
Pressing the level adjustment switch in the lower control panel control unit (N72) enables a selection to be made to match speed between normal level NN, a raised level EN1 and the highest level EN2, whereby each press induces a change to another level.
Any pressing of the level adjustment switch is read in by the lower control panel control unit and transmitted over the interior CAN to the electronic ignition switch control unit (N73). The electronic ignition switch control unit sends the signal over the engine compartment-CAN to the ABC control unit. Actuation of the light emitting diodes (LED) in the level adjustment switch ensues inversely.
The instrument cluster (A1) saves the switch position, so that following a restart the same setting is adopted as before ignition OFF. If the vehicle is in a normal level NN condition, both LEDs are switched off.
If the vehicle exceeds a defined speed threshold, the raised vehicle level is adapted (i.e. resumed) according to the increasing vehicle speed.
In the process the driver's level choice is not erased. The vehicle level is raised again as speed drops. The LEDs are actuated to match the preset level.
Vehicle level (without code (494) USA version):
Comfort setting:
NN -4 mm
EN1 +21 mm
EN2 +46 mm
Sport setting:
NN -19 mm
EN1 +21 mm
EN2 +46 mm
If the vehicle speed exceeds or drops below a defined speed threshold, the vehicle level is lowered or raised:
0 km/h NN -4 mm
65 km/h NN -4 mm
100 km/h NN -19 mm
0 km/h EN1 +21 mm
30 km/h EN1 +21 mm
140 km/h EN1 -4 mm
0 km/h EN2 +46 mm
30 km/h EN2 +46 mm
60 km/h EN2 +16 mm
140 km/h EN2 -4 mm
Vehicle level (with code (494) USA version):
Comfort setting:
NN -7 mm
EN1 +8 mm
EN2 +18 mm
Sport setting:
NN -19 mm
EN1 +8 mm
EN2 +18 mm
If the vehicle speed exceeds or drops below a defined speed threshold, the vehicle level is lowered or raised:
0 km/h NN -7 mm
65 km/h NN -7 mm
100 km/h NN -19 MM
0 km/h EN1 +8 mm
30 km/h EN1 +8 mm
140 km/h EN1 -7 mm
0 km/h EN2 +18 mm
30 km/h EN2 +18 mm
60 km/h EN2 +4 mm
140 km/h EN2 -7 mm
Additional function requirements for pressure supply, function
^ Circuit 61 ON
Pressure supply, function
A radial piston pump is used to supply the necessary pressure.
Like the power steering pump, it is part of the tandem pump and is driven by the engine via a belt drive.
The hydraulic oil is drawn out of the oil reservoir.
The ABC suction restrictor valve mounted onto the pump regulates the intake volume and thus the pressure for the system.
The oil quantity is determined dependent on the driving situation and cooled by means of an oil cooler.
The oil is delivered from the pump to the ABC front axle valve unit, to the ABC rear axle valve unit, to the rear axle central reservoir and to the front axle central reservoir.
The system pressure is recorded by the ABC pressure sensor and evaluated by the ABC control unit.
Lock position function sequence
So that when the vehicle is raised intentionally, e.g. with a jack, oil is not continuously drained out of the hydraulic suspension struts back into the return circuit, in order to lower the vehicle, it is necessary to automatically detect this unloading of the wheels and from it to derive a blocking position.
If the ABC control unit sets the blocking position, the control valves are no longer actuated and the following valves are closed:
- Left front suspension strut blocking valve (Y36/1y2)
- Right front suspension strut blocking valve (Y36/1y4)
- Left rear suspension strut blocking valve (Y36/2y2)
- Right rear suspension strut blocking valve (Y36/2y4)
If the ABC control unit receives left front and left right wheel speed signals with v > 0 km/h, from the ESP, SPS [PML] and BAS control unit (N47-5) over the engine compartment CAN, the blocking position is automatically canceled.
The wheel speed signals for determining the speed are read in by the SBC hydraulic unit (A7/3) and forwarded over the electrohydraulic brake CAN to the ESP, SPS [PML] and BAS control unit.
Suspension setting function requirements, function
^ Circuit 61 ON
Suspension setting function sequence
The driver can press the ABC Sport switch in the lower control panel control unit to select between a comfort-oriented and a sporty performance map.
The sporty performance map is indicated by a function LED integrated into the switch.
Pressing the ABC Sport switch again causes the performance map to change for the suspension from sporty to comfort-oriented. The function LED in the switch is switched off.
If the ABC Sport switch is pressed, the lower control panel control unit reads it in and forwards the signal over the interior CAN to the electronic ignition switch control unit. The electronic ignition switch control unit sends the signal over the engine compartment CAN to the ABC control unit.
Actuation of the function LED in the ABC Sport switch takes place in the following direction.
The ABC control unit saves the switch position, so that following a restart the same performance map is adopted as before ignition OFF.
Function requirements for system and warning messages
^ C. 15R On
System and warning messages function sequence
The left multifunction display (A1p13) and right multifunction display (A1p15) of the instrument cluster displays system and warning messages with instructions for the driver.
To display the messages the ABC control unit sends according messages over the engine compartment-CAN to the instrument cluster. There are three system messages or warning messages with different fault priority classes.
The fault priority classes differ mainly with respect to the various acknowledgment options for the driver.
Texts displayed in instrument cluster:
Warning messages:
- Malfunction
- Vehicle rises
- STOP, car too low
- Level selection cleared
- Active Body Control COMFORT
- Active Body Control SPORT
Fault messages:
- Malfunction
- Vehicle, rising, wait briefly
- STOP, malfunction
