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Home >> Mercedes Benz >> 2020 >> S450 Base >> Repair and Diagnosis >> Suspension >> Suspension Control Systems >> Suspension - 222 Chassis (1 Of 2) >> Basic Knowledge >> Active Body Control (ABC), Function >> Active Body Control (ABC), Function - GF32.50-P-0001LF

Active Body Control (ABC), Function - GF32.50-P-0001LF

Model 217 

With Code 487 (MAGIC BODY CONTROL) 

Model 222 

up to model year 2018 

With Code 487 (MAGIC BODY CONTROL) 

G15299322Courtesy of MERCEDES-BENZ USA

Block diagram 

G15299323Courtesy of MERCEDES-BENZ USA

Hydraulic diagram 

Function requirements, general 

IMPORTANT The circuit status is sent by the electronic ignition lock control unit over the chassis FlexRay to the Active Body Control, control unit.

General 

The Active Body Control (ABC) system is a full-bearing suspension system, i.e., the system uses four hydraulic suspension struts to actively build up pressure at each wheel.

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 Active Body Control, control unit.

IMPORTANT The system pressure is generated by the tandem pump. The ABC throttle valve and the ABC switchover valve, which are actuated by the Active Body Control (ABC) control unit, are located here.

When the ABC switchover valve is closed, actuation of the ABC throttle valve regulates the tandem pump delivery rate and thereby also the system pressure. Depending on the operating condition, the ABC switchover valve can also switch the tandem pump to unpressurized, whereupon oil is not pumped to the high-pressure circuit. As soon as the system pressure falls below 170 bar, the ABC switchover valve closes immediately. The ABC throttle valve is opened by opened by regulating the pressure as required.

By integrating the ABC switchover valve, the power output of the combustion engine to the tandem pump can be reduced, and a fuel saving achieved.

The ABC system contains the following sensors and actuators:

The active ABC suspension is different from other systems in that it uses dynamically-adjustable hydraulic cylinders in the suspension struts and does not use stabilizer bars like the conventional suspensions.

The hydraulic cylinders are arranged in a row and connected to the suspension springs, and use displacement to generate forces that counteract wheel load fluctuations. This makes it possible to minimize the body acceleration and, when cornering, to almost completely compensate for body rolling motions up to maximum lateral acceleration. Furthermore, it is also possible to adapt the vehicle level to the various speeds when driving. The Active Body Control (ABC) control unit continuously adapts the suspension and damping characteristic to the driving condition at any given time.

The following values can be recorded with the aid of a sensor system:

The actual values for the sensor system, longitudinal acceleration, steering wheel angle, vehicle speed and the load condition are continuously processed, to evaluate the sprung mass vibrations, vehicle level, system pressure and the position of the suspension strut position, to then activate the actuators correspondingly.

Advantages of ABC system compared to conventional suspension:

IMPORTANT The steering wheel angle is recorded by the steering wheel angle sensor, read in by the steering column tube module control unit and sent to the Active Body Control, control unit over the chassis FlexRay.

The ABC system consists of the following subfunctions:

Function requirements for wake-up mode 

Function sequence for wake-up mode 

The Active Body Control, control unit is directly activated by the electronic ignition lock control unit. The required data (signals when opening a door from the left front door first detent position microswitch, from the right front door first detent position microswitch, from the left rear door first detent position microswitch (except model 217), from the right rear door first detent position microswitch (except model 217) or from the trunk lid lock main catch switch or when opening the trunk) is received by the electronic ignition lock control unit from the rear SAM control unit, left front door control unit, right front door control unit, left rear door control unit (except model 217) and from the right rear door control unit (except model 217) over the interior CAN.

The wake-up mode is canceled as soon as the engine is started and the Active Body Control (ABC) control unit changes into normal mode.

Function requirements for initial test 

Function sequence for initial test 

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 sequence of wake-up mode already have to be checked during the transition to wake-up mode.

Function requirements for ABC closed-loop control 

Function sequence for ABC closed-loop control 

The stereo multifunction camera records pictures of the road and calculates the elevation profile based on the lane for the left and right sides of the vehicle. The stereo multifunction camera sends the data to the Active Body Control, control unit via chassis FlexRay.

The Active Body Control (ABC) control unit continuously activates the following regulation valves:

If hydraulic fluid is supplied to the suspension strut through a regulation valve when the shutoff valve is open, then the vehicle level or the actuator force at the wheel in question may increase. Inversely, the flow of oil from the suspension strut can lower the level or reduce the actuator force, depending on the level of road activation or the driving condition.

Pressing the vehicle level button in the Audio/COMAND control panel enables a speed-dependent selection to be made between normal level (NN) and a raised level (EN), whereby each press induces another change to a different level.

IMPORTANT If the vehicle is at standstill and if the engine was switched off using the ECO start/stop function, pressing the vehicle level button and changing level from normal level (NN) to raised level (EN) will cause the engine to start.

The engine is not started when the level changes from raised (EN) to normal (NN).

The actuation signal of the vehicle level button is read in by the Audio/COMAND control panel and sent to the COMAND controller unit over the telematics CAN. The COMAND controller unit forwards the signal to the Active Body Control, control unit via user interface CAN and chassis FlexRay with the electronic ignition lock control unit interface. The actuation of the LED in the vehicle level button takes place in the opposite way.

The Active Body Control (ABC) control unit saves the switch position, so that for a new start, the same position is assumed as before ignition off. If the vehicle is in NN condition, the LED is switched off.

A raised vehicle level is reduced as speed increases and under the following conditions:

In the process the driver's level choice is deleted. For the next ignition cycle, the Active Body Control, control unit starts at NN.

The level characteristics for normal (NN) and raised (EN) level are speed-dependent. This means that the Active Body Control (ABC) control unit continuously lowers the vehicle as speed rises or raises the level as speed drops.

Vehicle level (except code 494 (USA version))    
v [km/h] NN [mm] EN [mm]
0 -6 +44
30 -6 +44
65 -6 -6
100 -19 -6
140 -19 -19
Vehicle levels (with code 494 (USA version))    
v [km/h] Normal level (NN) [mm] Raised level (EN) [mm]
0 -6 +30
30 -6 +30
65 -6 -6
100 -19 -6
140 -19 -19

If the vehicle is parked in the Sport transmission mode, then it is lowered another 10 mm when normal (NN) level is selected. For vehicles with CODE 494 (USA version), there is no level lowering to normal (NN) and Sport driver setting.

Function requirement for pressure supply function 

Function sequence for pressure supply 

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 ABC system pressure is split up into three conditions. When the oil or system pressure requirement is low on smooth roads and when driving straight ahead, the ABC switchover valve is opened as of a system pressure > 180 bar. If the system pressure drops, e.g. because of higher speeds, below the speed-dependent system pressure threshold characteristic of 170 bar, the ABC switchover valve is closed again and pressure is built up with the ABC throttle valve closed.

If the oil requirement increases because of significant excitation caused by the road surface or when cornering with higher lateral acceleration, the pressure is built up by regulated actuation of the ABC throttle valve. If the vehicle is at a standstill and if the engine is idling, the ABC switchover valve is closed, to avoid any engine speed fluctuations. The hydraulic fluid is sucked out of the oil reservoir and routed back over the return line and the oil cooler. The ABC throttle valve mounted onto the tandem pump regulates the suction cross section and thus the intake volume for the system. The ABC switchover valve can also be used to switch the pump to unpressurized circulation, whereupon the pump no longer pumps any hydraulic fluid to the high pressure circuit. The hydraulic fluid is delivered from the tandem 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. To buffer the large oil flows in the return line, a return flow reservoir is also installed, which prevents pressure peaks and noises.

The system pressure is recorded by the ABC pressure sensor and evaluated by the Active Body Control (ABC) control unit.

Function sequence for locking position 

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 Active Body Control (ABC) control unit sets the blocking position, the control valves are no longer actuated and the following valves are closed:

If the Active Body Control, control unit receives wheel speed signals with v >0 km/h over the suspension FlexRay, or if the transmission is in the N position without electric parking brake and when the engine is running, the ABC closed loop control integrated into the Active Body Control, control unit is activated and the locking position is automatically canceled.

IMPORTANT The wheel speed signals for calculating the speed are recorded by the left front axle rpm sensor, right front axle rpm sensor, left rear axle rpm sensor and right rear axle rpm sensor, read in by the Electronic Stability Program control unit and sent to the Active Body Control, control unit via chassis FlexRay.

Function requirements for suspension tuning, function 

Function sequence for suspension tuning 

The driver can press the Comfort/Sport button in the Audio/COMAND control panel to select between a comfort-oriented and a sporty characteristics map. Each active characteristics map is indicated by the function LEDs integrated into the Comfort/Sport button. Pressing the Comfort/Sport button again causes the characteristics map to change for the suspension from sporty to comfort-oriented. The actuation signal of the Comfort/Sport button is read in by the Audio/COMAND control panel. The Audio/COMAND control panel sends the signal to the Active Body Control, control unit via telematics CAN, COMAND controller unit, user interface CAN, electronic ignition lock control unit and chassis FlexRay. The function LEDs in the Comfort/Sport button is actuated in the opposite way.

The Active Body Control (ABC) control unit saves the button position, so that for a new start, the same characteristics map is assumed as before ignition off.

Function sequence for CURVE (for model 217, except AMG vehicles) 

In the CURVE transmission mode, the vehicle tilts actively into the curve. The ride comfort on curves is increased through this curve function and the comfortable suspension tuning. CURVE is available in a vehicle speed range between 40 km/h and 180 km/h.

Pressing the Comfort/Sport several times in Audio/COMAND control panel until both LEDs in the button light up, activates the CURVE function.

The signal of the Comfort/Sport button is read in by the Audio/COMAND control panel and sent over the telematics CAN, COMAND controller unit, the user interface CAN, electronic ignition lock control unit and the suspension FlexRay to the Active Body Control, control unit.

Function sequence for load detection 

If the vehicle is loaded, the Active Body Control, control unit detects the change of forces at each wheel with the help of the signals from the level sensors and the pressure sensors. The anti-roll characteristics and the active body damping react to the changed forces. For this, the Active Body Control, control unit actuates the regulating valves in the ABC front axle valve unit and ABC rear axle valve unit and adjusts the dampers for higher load. The load is constantly adjusted.

IMPORTANT The total effect of the load can never be compensated for; the driver thus still realizes that he/she is driving a laden vehicle.

Function requirement for crosswind compensation 

Function sequence for crosswind compensation 

The lateral forces caused by the crosswind can be calculated using the signals of steering wheel angle, yaw rate, lateral acceleration, vehicle speed and the mass inertia of the vehicle. The signals are provided to the Active Body Control, control unit on chassis FlexRay.

Based on the calculated transverse force caused by the crosswind, lane deviation caused by the chassis being under tension can be reduced. In case of varying wheel loads at one axle, a rotary motion of the vehicle can be generated by means of toe-in at the front and rear axles, which counteracts the crosswind.

Function requirements for run-on mode 

Function sequence for run-on mode 

After the ignition is switched off, the run-on mode is active for t = 1 minute. Within this time, it is possible to lower the vehicle using the vehicle level button or via the menu in the instrument cluster.

If, after switching the ignition off, the sporty characteristics map was selected for the vehicle using the Comfort/Sport button, the vehicle lowers automatically by 10 mm.

Function requirements for system and warning messages 

Function sequence for system and warning messages 

System and warning messages with instructions for the driver are displayed in the instrument cluster.

In order to output the messages, the Active Body Control, control unit sends appropriate messages over the suspension FlexRay and the user interface CAN with the electronic ignition lock control unit interface 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:

  Electrical function schematic for Active Body Control (ABC)   PE32.50-P-2050-97SEA
  Overview of system components, Active Body Control (ABC)   GF32.50-P-9997LF 
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